Evoqua Water Technologies (AQUA) 10-Q 5 May 21 2021 Q2 Quarterly report Financial data

Cover

Cover - shares	6 Months Ended
	Mar. 31, 2021	Apr. 30, 2021
Cover [Abstract]
Amendment Flag	false
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Title of 12(b) Security	Common Stock, par value $0.01 per share
Entity Incorporation, State or Country Code	DE
Document Quarterly Report	true
Document Type	10-Q
Document Period End Date	Mar. 31, 2021
Document Transition Report	false
Entity File Number	001-38272
Entity Registrant Name	EVOQUA WATER TECHNOLOGIES CORP.
Entity Tax Identification Number	46-4132761
Entity Address, Address Line One	210 Sixth Avenue
Entity Address, Postal Zip Code	15222
Entity Address, City or Town	Pittsburgh,
Entity Address, State or Province	PA
City Area Code	724
Local Phone Number	772-0044
Trading Symbol	AQUA
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		119,900,432
Document Fiscal Period Focus	Q2
Document Fiscal Year Focus	2021
Entity Central Index Key	0001604643
Current Fiscal Year End Date	--09-30

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2021	Sep. 30, 2020
ASSETS
Current assets	$ 717,132	$ 695,712
Cash and cash equivalents	222,718	193,001
Receivables, net	227,343	260,479
Inventories, net	156,787	142,379
Contract assets	74,801	80,759
Prepaid and other current assets	34,491	18,715
Income tax receivable	992	379
Property, plant, and equipment, net	371,868	364,461
Goodwill	404,393	397,205
Intangible assets, net	299,318	309,967
Deferred income taxes, net of valuation allowance	1,661	3,639
Operating lease right-of-use assets, net	47,591	45,965
Other non‑current assets	37,836	27,509
Total assets	1,879,799	1,844,458
LIABILITIES AND EQUITY
Current liabilities	346,573	349,555
Accounts payable	144,613	153,890
Current portion of debt, net of deferred financing fees	21,343	14,339
Contract liabilities	36,894	26,259
Product warranties	6,714	6,115
Accrued expenses and other liabilities	134,692	143,389
Income tax payable	2,317	5,563
Non‑current liabilities	1,008,341	1,012,840
Long-term debt, net of deferred financing fees	859,692	861,695
Product warranties	1,989	1,724
Obligation under operating leases	39,174	37,796
Other non‑current liabilities	96,007	98,456
Deferred income taxes	11,479	13,169
Total liabilities	1,354,914	1,362,395
Commitments and Contingent Liabilities (Note 19)
Shareholders’ equity
Common stock, par value $0.01: authorized 1,000,000 shares; issued 121,442 shares, outstanding 119,778 at March 31, 2021; issued 119,486 shares, outstanding 117,291 at September 30, 2020	1,215	1,189
Treasury stock: 1,664 shares at March 31, 2021 and 2,195 shares at September 30, 2020	(2,837)	(2,837)
Additional paid-in capital	564,034	564,928
Retained deficit	(51,195)	(62,664)
Accumulated other comprehensive income (loss), net of tax	12,009	(20,472)
Total Evoqua Water Technologies Corp. equity	523,226	480,144
Non-controlling interest	1,659	1,919
Total shareholders’ equity	524,885	482,063
Total liabilities and shareholders’ equity	$ 1,879,799	$ 1,844,458

Consolidated Balance Sheets Con

Consolidated Balance Sheets Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2021	Sep. 30, 2020
Statement of Financial Position [Abstract]
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, authorized (in shares)	1,000,000,000	1,000,000,000
Common stock, issued (in shares)	121,442,000	119,486,000
Common stock, outstanding (in shares)	119,778,000	117,291,000
Treasury stock (in shares)	1,664,000	2,195,000

Unaudited Consolidated Statemen

Unaudited Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Revenues [Abstract]
Revenue from product sales and services	$ 346,564	$ 351,663	$ 668,757	$ 697,768
Cost of Revenue [Abstract]
Cost of product sales and services	(240,645)	(240,457)	(467,493)	(480,847)
Gross profit	105,919	111,206	201,264	216,921
Operating Expenses [Abstract]
General and administrative expense	(52,928)	(62,130)	(95,211)	(107,900)
Sales and marketing expense	(33,830)	(33,976)	(67,758)	(71,990)
Research and development expense	(3,393)	(3,189)	(6,516)	(6,873)
Total operating expenses	(90,151)	(99,295)	(169,485)	(186,763)
Other operating income	511	9,518	991	61,238
Other operating expense	(101)	(274)	(358)	(549)
Operating profit (loss)	16,178	21,155	32,412	90,847
Interest expense	(8,395)	(13,252)	(17,068)	(26,835)
Income before income taxes	7,783	7,903	15,344	64,012
Income tax (expense) benefit	(2,701)	7	(3,785)	(2,596)
Net income	5,082	7,910	11,559	61,416
Net income attributable to non‑controlling interest	46	98		459
Net income attributable to Evoqua Water Technologies Corp.	$ 5,036	$ 7,812	$ 11,469	$ 60,957
Basic income per common share	$ 0.04	$ 0.07	$ 0.10	$ 0.52
Diluted income per common share	$ 0.04	$ 0.06	$ 0.09	$ 0.50
Revenue from product sales
Revenues [Abstract]
Revenue from product sales and services	$ 202,466	$ 205,969	$ 382,481	$ 402,529
Cost of Revenue [Abstract]
Cost of product sales and services	(144,521)	(144,156)	(275,582)	(284,612)
Revenue from service
Revenues [Abstract]
Revenue from product sales and services	144,098	145,694	286,276	295,239
Cost of Revenue [Abstract]
Cost of product sales and services	$ (96,124)	$ (96,301)	$ (191,911)	$ (196,235)

Unaudited Consolidated Statem_2

Unaudited Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Other comprehensive (loss) income
Net income	$ 5,082	$ 7,910	$ 11,559	$ 61,416
Foreign currency translation adjustments	26,891	(14,724)	22,014	(6,667)
Unrealized derivative gain (loss) on cash flow hedges, net of tax	9,091	(162)	10,093	(211)
Change in pension liability, net of tax	110	235	374	471
Total other comprehensive income (loss)	36,092	(14,651)	32,481	(6,407)
Less: Comprehensive income attributable to non‑controlling interest	(46)	(98)	(90)	(459)
Comprehensive income (loss) attributable to Evoqua Water Technologies Corp.	$ 41,128	$ (6,839)	$ 43,950	$ 54,550

Unaudited Consolidated Statem_3

Unaudited Consolidated Statements of Changes in Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment [Member]	Common Stock	Treasury Stock	Additional Paid‑in Capital	Retained Deficit	Retained DeficitCumulative Effect, Period of Adoption, Adjustment [Member]	Accumulated Other Comprehensive Loss	Non‑controlling Interest
Common stock issued at the beginning of the period (shares) at Sep. 30, 2019			116,008,000
Stockholders' equity, balance at the beginning of the period at Sep. 30, 2019	$ 365,822	$ (1,337)	$ 1,154	$ (2,837)	$ 552,422	$ (174,976)	$ (1,337)	$ (13,004)	$ 3,063
Treasury stock, balance at the beginning of the period (in shares) at Sep. 30, 2019				1,664,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (in shares)			3,062,000	(531,000)
Issuance of common stock, cost	15,370		$ 31		15,339
Dividends paid to non-controlling interest	(1,450)								(1,450)
Equity based compensation expense	5,984				5,984
Divestiture of Lange product line	(16,895)				(16,895)
Net income	61,416					60,957			459
Other comprehensive income (loss)	(6,407)							(6,407)
Common stock issued at the end of the period (shares) at Mar. 31, 2020			119,070,000
Stockholders' equity, balance at the end of the period at Mar. 31, 2020	422,503		$ 1,185	$ (2,837)	556,850	(115,356)		(19,411)	2,072
Treasury stock, balance at the end of the period (in shares) at Mar. 31, 2020				2,194,000
Common stock issued at the beginning of the period (shares) at Dec. 31, 2019			117,653,000
Stockholders' equity, balance at the beginning of the period at Dec. 31, 2019	415,130	$ 686	$ 1,170	$ (2,837)	543,237	(123,854)	$ 686	(4,760)	2,174
Treasury stock, balance at the beginning of the period (in shares) at Dec. 31, 2019				2,083,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (in shares)			1,417,000	111,000
Issuance of common stock, cost	11,324		$ 15		11,309
Dividends paid to non-controlling interest	(200)								(200)
Equity based compensation expense	2,304				2,304
Net income	7,910					7,812			98
Other comprehensive income (loss)	(14,651)							(14,651)
Common stock issued at the end of the period (shares) at Mar. 31, 2020			119,070,000
Stockholders' equity, balance at the end of the period at Mar. 31, 2020	$ 422,503		$ 1,185	$ (2,837)	556,850	(115,356)		(19,411)	2,072
Treasury stock, balance at the end of the period (in shares) at Mar. 31, 2020				2,194,000
Common stock issued at the beginning of the period (shares) at Sep. 30, 2020	119,486,000		119,486,000
Stockholders' equity, balance at the beginning of the period at Sep. 30, 2020	$ 482,063		$ 1,189	$ (2,837)	564,928	(62,664)		(20,472)	1,919
Treasury stock, balance at the beginning of the period (in shares) at Sep. 30, 2020	2,195,000			2,195,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (in shares)			1,956,000	530,000
Issuance of common stock, cost	$ (7,101)		$ 26		(7,127)
Dividends paid to non-controlling interest	(350)								(350)
Equity based compensation expense	6,233				6,233
Net income	11,559					11,469			90
Other comprehensive income (loss)	$ 32,481
Common stock issued at the end of the period (shares) at Mar. 31, 2021	121,442,000		121,442,000
Stockholders' equity, balance at the end of the period at Mar. 31, 2021	$ 524,885		$ 1,215	$ (2,837)	564,034	(51,195)		12,009	1,659
Treasury stock, balance at the end of the period (in shares) at Mar. 31, 2021	1,664,000			1,664,000
Common stock issued at the beginning of the period (shares) at Dec. 31, 2020			120,750,000
Stockholders' equity, balance at the beginning of the period at Dec. 31, 2020	$ 501,961		$ 1,202	$ (2,837)	582,197	(56,231)		(24,083)	1,713
Treasury stock, balance at the beginning of the period (in shares) at Dec. 31, 2020				2,196,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (in shares)			692,000	(532,000)
Issuance of common stock, cost	(21,364)		$ 13		(21,377)
Dividends paid to non-controlling interest	(100)								(100)
Equity based compensation expense	3,214				3,214
Net income	5,082					5,036			46
Other comprehensive income (loss)	$ 36,092							36,092
Common stock issued at the end of the period (shares) at Mar. 31, 2021	121,442,000		121,442,000
Stockholders' equity, balance at the end of the period at Mar. 31, 2021	$ 524,885		$ 1,215	$ (2,837)	$ 564,034	$ (51,195)		$ 12,009	$ 1,659
Treasury stock, balance at the end of the period (in shares) at Mar. 31, 2021	1,664,000			1,664,000

Unaudited Consolidated Statem_4

Unaudited Consolidated Statements of Changes in Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating activities
Net income	$ 11,559	$ 61,416
Reconciliation of net income to cash flows provided by operating activities:
Depreciation and amortization	54,607	52,514
Write off of Deferred Debt Issuance Cost	0	1,795
Amortization of deferred financing fees (includes $0 and $1,795 write off of deferred financing fees)	1,044	3,103
Deferred income taxes	476	(1,209)
Share-based compensation	6,233	5,984
Loss on sale of property, plant and equipment	807	170
Loss (gain) on sale of business		(68,051)
Foreign currency exchange (gains) losses on intercompany loans and other non-cash items	(3,659)	1,514
Changes in assets and liabilities
Accounts receivable	36,221	7,256
Inventories	(14,091)	(17,800)
Contract assets	6,553	(5,377)
Prepaids and other current assets	(9,921)	(3,715)
Accounts payable	(9,799)	6,004
Accrued expenses and other liabilities	(9,089)	60
Contract liabilities	9,829	(4,920)
Income taxes	(3,948)	2,140
Other non‑current assets and liabilities	(13,955)	(252)
Net cash provided by operating activities	63,058	38,837
Investing activities
Purchase of property, plant and equipment	(36,297)	(38,759)
Purchase of intangibles	(539)	(622)
Proceeds from sale of property, plant and equipment	640	271
Proceeds from sale of business, net of cash of $0 and $12,117		118,894
Acquisitions	(8,743)	(11,164)
Net cash (used in) provided by investing activities	(44,042)	68,620
Financing activities
Issuance of debt, net of deferred issuance costs	13,993	8,212
Borrowings under credit facility	0	2,597
Repayment of debt	(10,036)	(109,333)
Repayment of finance lease obligation	(6,901)	(6,694)
Payment of earn-out related to previous acquisitions	0	(175)
Proceeds from issuance of common stock	13,430	8,333
Taxes paid related to net share settlements of share-based compensation awards	(1,863)	(9,817)
Distribution to non‑controlling interest	(350)	(1,450)
Net cash provided by (used in) financing activities	8,273	(108,327)
Effect of exchange rate changes on cash	2,428	(516)
Change in cash and cash equivalents	29,717	(1,386)
Cash and cash equivalents
Beginning of period	193,001	109,881
End of period	222,718	108,495
Supplemental disclosure of cash flow information
Cash paid for taxes	5,457	2,133
Cash paid for interest	14,647	22,953
Non‑cash investing and financing activities
Finance lease transactions	9,044	4,308
Operating lease transactions	7,993	10,076
Option and Purchase Right	$ 0	$ 7,167

Unaudited Consolidated Statem_5

Unaudited Consolidated Statements of Changes in Cash Flows Unaudited Supplemental Disclosure of Cash Flow Information (Parenthetical) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement of Cash Flows [Abstract]
Cash divested with sale of business	$ 0	$ 12,117

Description of the Company and

Description of the Company and Basis of Presentation	6 Months Ended
	Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of the Company and Basis of Presentation	Description of the Company and Basis of Presentation Background Evoqua Water Technologies Corp. (referred to herein as the “Company” or “EWT”) is a holding company and does not conduct any business operations of its own. The Company was incorporated on October 7, 2013. On January 15, 2014, the Company acquired through its wholly owned subsidiaries, EWT Holdings II Corp. (“EWT II”) and EWT Holdings III Corp. (“EWT III”), all of the outstanding shares of Siemens Water Technologies, a group of legal entity businesses formerly owned by Siemens AG (“Siemens”). The stock purchase closed on January 15, 2014 and was effective January 16, 2014 (the “Acquisition”). On November 6, 2017, the Company completed its initial public offering (“IPO”). On December 4, 2020, the Company completed a secondary public offering, pursuant to which 12,000 shares of common stock were sold by certain selling shareholders. On February 11, 2021, the Company completed an additional secondary public offering, pursuant to which 16,383 shares of common stock were sold by certain selling shareholders. Upon completion of these offerings, AEA Investors LP disposed of all of their shares of the Company’s common stock. The Company did not receive any proceeds from the sale of shares by the selling shareholders in either of these secondary public offerings. The Business EWT provides a wide range of product brands and advanced water and wastewater treatment systems and technologies, as well as mobile and emergency water supply solutions and service contract options through its branch network. Headquartered in Pittsburgh, Pennsylvania, EWT is a multinational corporation with operations in the United States (“U.S.”), Canada, the United Kingdom (“UK”), the Netherlands, Germany, Australia, the People’s Republic of China, Singapore, the Republic of Korea and India. The Company is organizationally structured into two reportable operating segments for the purpose of making operational decisions and assessing financial performance: (i) Integrated Solutions and Services and (ii) Applied Product Technologies. Basis of Presentation The accompanying Unaudited Consolidated Financial Statements have been prepared in accordance with accounting principles generally accepted in the U.S. (“GAAP”). All intercompany transactions have been eliminated. Unless otherwise specified, all dollar and share amounts in these notes are referred to in thousands. The interim Unaudited Consolidated Financial Statements have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). Certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such SEC rules. We believe that the disclosures made are adequate to make the information presented not misleading. In our opinion, all adjustments considered necessary for a fair presentation of the financial statements have been included, and all adjustments are of a normal and recurring nature. We consistently applied the accounting policies described in our Annual Report on Form 10-K for the fiscal year ended September 30, 2020, as filed with the SEC on November 20, 2020 (“2020 Annual Report”), in preparing these Unaudited Consolidated Financial Statements, with the exception of accounting standard updates described in Note 2, “Recent Accounting Pronouncements.” These Unaudited Consolidated Financial Statements should be read in conjunction with the audited financial statements and the notes included in our 2020 Annual Report. Certain prior period amounts have been reclassified to conform to the current period presentation. Correction of Immaterial Errors During the quarter ending March 31, 2021, the Company identified errors related to the reporting of tax remittances associated with certain equity awards, resulting in a classification error of $18,669 between additional paid in capital and accumulated other comprehensive loss. Management recorded the correction to additional paid in capital and accumulated other comprehensive balances during the quarter ending March 31, 2021. Management considered both the quantitative and qualitative factors within the provisions of SEC Staff Accounting Bulletin No. 99, Materiality , and Staff Accounting Bulletin No. 108, Considering the Effects of Prior Year Misstatements when Quantifying Misstatements in Current Year Financial Statements . Based on evaluation of the errors, management has concluded that the prior period errors were immaterial to the previously issued financial statements. As a result of that classification error, management also identified a second, related immaterial classification error for the understatement of net cash provided by operating cash flows of $18,669 and an overstatement of net cash provided by financing activities of $18,669 for the period from October 1, 2019 to September 30, 2020. The Company has elected to voluntarily correct the identified immaterial classification error in the prior period Unaudited Consolidated Statements of Changes to Cash Flows to enhance comparability. In doing so, balances in the Unaudited Consolidated Statements of Changes to Cash Flows included in this Form 10-Q have been adjusted to reflect the voluntary immaterial classification error correction of $16,854 between financing and operating in the prior period. Future filings that include prior periods will be corrected, as needed, when filed. The correction of the above classification errors did not have any effect on the Unaudited Consolidated Statements of Operations in any of the periods previously presented.

Recent Accounting Pronouncement

Recent Accounting Pronouncements	6 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements Accounting Pronouncements Not Yet Adopted In March 2020, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting (“ASU 2020-04”), which was amended by the subsequent issuance in January 2021 of ASU 2021-01, Reference Rate Reform (Topic 848): Scope (“ASU 2021-01”). ASU 2020-04 became effective immediately and expires on December 21, 2022. ASU 2020-04 allows eligible contracts that are modified to be accounted for as a continuation of those contracts, permits companies to preserve their hedging accounting during the transition period and enables companies to make a one-time election to transfer or sell held-to-maturity debt securities that are affected by rate reform. ASU 2021-01 provides optional expedients and exceptions for contracts, hedging relationships and other transactions that reference the London Inter-Bank Offered Rate (“LIBOR”) or another reference rate expected to be discontinued because of reference rate reform, if certain criteria are met. The Company is currently assessing the impact of the adoption of ASU 2020-04 and ASU 2021-01 on the Company’s Unaudited Consolidated Financial Statements and related disclosures. Accounting Pronouncements Recently Adopted The Company adopted ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments on October 1, 2020 (“ASU 2016-13”). ASU 2016-13 requires entities to use a new forward-looking “expected loss” model that reflects expected credit losses, including credit losses related to trade receivables, and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates which generally will result in the earlier recognition of allowances for losses. The Company adopted ASU 2016-13 us ing a modified retrospective approach and determined that there was no cumulative-effect adjustment to its beginning Retained deficit on the Consolidated Balance Sheets. The adoption of this standard did not hav e a material impact on the Company’s Unaudited Consolidated Financial Statements. See Note 7, “Accounts Receivable” for further details and related disclosures. The following accounting pronouncements were adopted by the Company on October 1, 2020, and the adoptions did not have a material impact on the Company’s Unaudited Consolidated Financial Statements or disclosures: Accounting Standards Updates ASU 2020-03, Codification Improvements to Financial Instruments ASU 2018-19, Codification Improvements to Topic 326, Financial Instruments—Credit Losses ASU 2018-18, Collaborative Arrangements (Topic 808) Clarifying the Interaction between Topic 808 and Topic 606 ASU 2018-13, Fair Value Measurement (Subtopic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement

Variable Interest Entities

Variable Interest Entities	6 Months Ended
	Mar. 31, 2021
Equity Method Investments and Joint Ventures [Abstract]
Variable Interest Entity Disclosure	Variable Interest Entities Treated Water Outsourcing (“TWO”) is a joint venture between the Company and Nalco Water, an Ecolab company, in which the Company holds a 50% partnership interest. The Company is obligated to absorb all risk of loss up to 100% of the joint venture partner’s equity. As such, the Company fully consolidates TWO as a variable interest entity (“VIE”) under ASC Topic No. 810, Consolidation . The Company has not provided, and is not contractually required to provide, additional financial support to this entity, and the Company does not have the ability to use the assets of TWO to settle obligations of the Company’s other subsidiaries. The following provides a summary of TWO’s balance sheet as of March 31, 2021 and September 30, 2020, and summarized financial information for the three and six months ended March 31, 2021 and 2020. March 31, September 30, Current assets (includes cash of $1,552 and $2,088) $ 3,462 $ 4,016 Property, plant and equipment 1,024 1,145 Goodwill 2,206 2,206 Total liabilities (1,168) (1,324) Three Months Ended Six Months Ended 2021 2020 2021 2020 Total revenue $ 834 $ 1,210 $ 1,668 $ 3,852 Total operating expenses (732) (1,086) (1,469) (3,044) Income from operations $ 102 $ 124 $ 199 $ 808 On October 1, 2019, the Company acquired a 60% investment position in San Diego-based Frontier Water Systems, LLC (“Frontier”). The Frontier acquisition is a VIE because it has insufficient equity to finance its activities due to key assets being assigned to the Company upon acquisition. The Company is the primary beneficiary of Frontier because the Company has the power to direct the activities that most significantly affect Frontier’s economic performance. In addition, the Company entered into an agreement to purchase the remaining 40% interest in Frontier on or prior to March 30, 2024. This agreement (a) gave holders of the remaining 40% interest in Frontier (the “Minority Owners”) the right to sell to Evoqua up to approximately 10% of the outstanding equity in Frontier at a predetermined price, which right was exercisable by the Minority Owners between January 1, 2021 and February 28, 2021 (the “Option”), and (b) obligates the Company to purchase and the Minority Owners to sell all of the Minority Owners’ remaining interest in Frontier at the fair market value at the time of sale on or prior to March 30, 2024 (the “Purchase Right”). The Purchase Right may be exercised early by the Minority Owners. The agreement to purchase the remaining interest was determined to be financing due to the mandatory Purchase Right, as per ASC Topic 480, Distinguishing Liabilities From Equity , and as such, the Company recognized a liability for the remaining 40% interest. During the three months ended March 31, 2021, the Minority Owners exercised the Option, and on April 8, 2021 the Company completed the purchase of an additional 8% of the outstanding equity in Frontier for approximately $1,490. This amount was reclassified from Other non‑current liabilities to Accrued expenses and other liabilities on the Consolidated Balance Sheets during the three months ended March 31, 2021. As a result, the Company’s ownership position in Frontier increased to 68%. Additionally, the Company fully consolidates Frontier as a VIE under ASC Topic No. 810, Consolidation . The following provides a summary of Frontier’s balance sheet as of March 31, 2021 and September 30, 2020, and summarized financial information for the three and six months ended March 31, 2021 and 2020. March 31, September 30, Current assets (includes cash of $1,182 and $1,675) $ 5,045 $ 4,024 Property, plant and equipment 3,094 3,159 Goodwill 1,798 1,798 Intangible assets, net 9,092 9,918 Total liabilities (5,095) (3,692) Three Months Ended Six Months Ended 2021 2020 2021 2020 Total revenue $ 2,078 $ 1,078 $ 2,848 $ 2,723 Total operating expenses (2,401) (2,364) (4,139) (4,301) Loss from operations $ (323) $ (1,286) $ (1,291) $ (1,578)

Acquisitions

Acquisitions	6 Months Ended
	Mar. 31, 2021
Business Combinations [Abstract]
Acquisitions and Divestitures	Acquisitions and Divestitures Acquisitions support the Company’s strategy of delivering a broad solutions portfolio with robust technology across multiple geographies and end markets. The Company continues to evaluate potential strategic acquisitions of businesses, assets and product lines and believes that capex-like, tuck-in acquisitions present a key opportunity within its overall growth strategy. On December 17, 2020, the Company acquired the industrial water business of Ultrapure & Industrial Services, LLC (“Ultrapure”) for $8,743 cash paid at closing. Ultrapure, based out of Texas, provides customers across multiple end markets with a variety of water treatment products and services, including service deionization, reverse osmosis, UV and ozonation. Ultrapure will strengthen the Company’s service capabilities in the Houston and Dallas markets and is a part of the Integrated Solutions and Services segment. During the six months ended March 31, 2021, the Company incurred approximately $229 in acquisition costs, which are included in General and administrative expense on the Unaudited Consolidated Statements of Operations. The accounting for the acquisition has not yet been completed because the Company has not finalized the valuations of the acquired assets, assumed liabilities and identifiable intangible assets, including goodwill. The preliminary opening balance sheet for Ultrapure is summarized as follows: Current assets $ 2,366 Property, plant and equipment 963 Goodwill 2,545 Intangible assets, net 3,751 Other non-current assets 22 Total assets acquired 9,647 Liabilities assumed (904) Net assets acquired $ 8,743 On March 1, 2021, the Company completed the divestiture of the Lange containment system, geomembrane and geosynthetic liner product line (the “Lange Product Line”) for $897 in cash at closing. The Lange Product Line was a part of the Integrated Solutions and Services segment. During the three months ended March 31, 2021, the Company recognized a loss of $191 on the divestiture.

Revenue

Revenue	6 Months Ended
	Mar. 31, 2021
Revenue from Contract with Customer [Abstract]
Revenue from Contract with Customer [Text Block]	Revenue Revenue Recognition The Company recognizes sales of products and services based on the five-step analysis of transactions as provided in ASU 2014-09, Revenue from Contracts with Customers (Topic 606) (“Topic 606”). For all contracts with customers, the Company first identifies the contract which usually is established when the customer’s purchase order is accepted or acknowledged. Next the Company identifies the performance obligations in the contract. A performance obligation is a promise in a contract to transfer a distinct good or service to the customer. The Company then determines the transaction price in the arrangement and allocates the transaction price to each performance obligation identified in the contract. The Company’s allocation of the transaction price to the performance obligations are based on the relative standalone selling prices for the goods and services contained in a particular performance obligation. The transaction price is adjusted for the Company’s estimate of variable consideration which may include discounts if the Company would fail to meet certain performance requirements, volume discounts or early payment discounts. To estimate variable consideration, the Company utilizes historical experience and known terms. Variable consideration in contracts for the three and six months ended March 31, 2021 was insignificant. For sales of aftermarket parts or products with a low level of customization and engineering time, the Company recognizes revenue at the time risks and rewards of ownership pass, which is generally when products are shipped or delivered to the customer as the Company has no obligation for installation. The Company considers shipping and handling services to be fulfillment activities and as such they do not represent separate performance obligations for revenue recognition. Sales of service arrangements are recognized as the services are performed. For certain arrangements where there is significant customization to the product and for long-term construction-type sales contracts, revenue may be recognized over time. In these instances, revenue is recognized using a measure of progress that applies an input method based on costs incurred in relation to total estimated costs. These arrangements include large capital water treatment projects, systems and solutions for municipal and industrial applications. The nature of the contracts is generally fixed price with milestone billings. In order for revenue to be recognized over a period of time, the product must have no alternative use and the Company must have an enforceable right to payment for the performance completed to date, including a normal profit margin, in the event of termination for convenience. If these two criteria are not met, revenue from these contracts will not be recognized until construction is complete. Contract revenue and cost estimates are reviewed and revised quarterly at a minimum and the cumulative effect of such adjustments are recognized in current operations. The amount of such adjustments has not been material. The Company has made accounting policy elections to exclude all taxes by governmental authorities from the measurement of the transaction price and that long-term construction-type sales contracts, or those contracts for products with significant customization that the total contract price is less than $100, will be recorded at the point in time when the construction is complete. Performance Obligations The Company elects to apply the practical expedient to exclude from this disclosure revenue related to performance obligations if the product has an alternative use and the Company does not have an enforceable right to payment for the performance completed to date, including a normal profit margin, in the event of termination for convenience. The Company maintains a backlog of confirmed orders, which totaled approximately $207,439 at March 31, 2021. This backlog represents the aggregate amount of the transaction price allocated to performance obligations that were unsatisfied or partially unsatisfied as of the end of the reporting period. The Company estimates that the majority of these performance obligations will be satisfied within the next twelve The recording of assets recognized from the costs to obtain and fulfill customer contracts primarily relate to the deferral of sales commissions. The Company’s costs incurred to obtain or fulfill a contract with a customer are classified as non-current assets and amortized to expense over the period of benefit of the related revenue. These costs are recorded within Cost of product sales and services. The amount of contract costs was insignificant at March 31, 2021. The Company offers standard warranties that generally do not represent a separate performance obligation. In certain instances, a warranty is obtained separately from the original equipment sale or the warranty provides incremental services and as such is treated as a separate performance obligation. Disaggregation of Revenue In accordance with Topic 606, the Company disaggregates revenue from contracts with customers into source of revenue, reportable operating segment and geographical regions. The Company determined that disaggregating revenue into these categories meets the disclosure objective in Topic 606, which is to depict how the nature, amount, timing and uncertainty of revenue and cash flows are affected by economic factors. Information regarding the source of revenue: Three Months Ended Six Months Ended 2021 2020 2021 2020 Revenue from contracts with customers recognized under Topic 606 $ 297,919 $ 314,994 $ 583,107 $ 623,596 Other (1) 48,645 36,669 85,650 74,172 Total $ 346,564 $ 351,663 $ 668,757 $ 697,768 (1) Other revenue relates to revenue recognized pursuant to ASU 2016-02, Leases (Topic 842) , mainly attributable to long term rentals. Information regarding revenue disaggregated by source of revenue and segment is as follows: Three Months Ended March 31, 2021 2020 Integrated Solutions and Services Applied Product Technologies Total Integrated Solutions and Services Applied Product Technologies Total Revenue from capital projects $ 52,093 $ 90,296 $ 142,389 $ 66,092 $ 75,214 $ 141,306 Revenue from aftermarket 32,501 27,576 60,077 31,901 32,762 64,663 Revenue from service 139,540 4,558 144,098 139,892 5,802 145,694 Total $ 224,134 $ 122,430 $ 346,564 $ 237,885 $ 113,778 $ 351,663 Six Months Ended March 31, 2021 2020 Integrated Solutions and Services Applied Product Technologies Total Integrated Solutions and Services Applied Product Technologies Total Revenue from capital projects $ 102,719 $ 167,185 $ 269,904 $ 120,712 $ 150,140 $ 270,852 Revenue from aftermarket 59,647 52,930 112,577 61,574 70,103 131,677 Revenue from service 276,485 9,791 286,276 283,737 11,502 295,239 Total $ 438,851 $ 229,906 $ 668,757 $ 466,023 $ 231,745 $ 697,768 Information regarding revenue disaggregated by geographic area is as follows: Three Months Ended Six Months Ended 2021 2020 2021 2020 United States $ 274,681 $ 290,273 $ 538,812 $ 567,990 Europe 31,527 30,381 52,812 56,493 Asia 26,976 12,720 49,581 31,462 Canada 10,636 16,319 21,815 33,882 Australia 2,744 1,970 5,737 7,941 Total $ 346,564 $ 351,663 $ 668,757 $ 697,768 Contract Balances The Company performs its obligations under a contract with a customer by transferring products and/or services in exchange for consideration from the customer. The Company receives payments from customers based on a billing schedule as established in its contracts. Contract assets relate to costs incurred to perform in advance of scheduled billings. Contract liabilities relate to payments received in advance of performance under the contracts. Change in contract assets and liabilities are due to the Company’s performance under the contract. The tables below provide a roll-forward of contract assets and contract liabilities balances for the periods presented: Six Months Ended Contract assets (a) 2021 2020 Balance at beginning of period $ 80,759 $ 73,467 Recognized in current period 147,593 172,228 Reclassified to accounts receivable (153,964) (166,535) Amounts related to sale of the Memcor product line — 2,710 Foreign currency 413 (621) Balance at end of period $ 74,801 $ 81,249 (a) Excludes receivable balances which are disclosed on the Consolidated Balance Sheets. Six Months Ended Contract Liabilities 2021 2020 Balance at beginning of period $ 26,259 $ 39,051 Recognized in current period 158,452 157,114 Amounts in beginning balance reclassified to revenue (20,703) (37,497) Current period amounts reclassified to revenue (127,684) (124,194) Amounts related to sale of the Memcor product line — (700) Foreign currency 570 (83) Balance at end of period $ 36,894 $ 33,691

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurement	Fair Value Measurements As of March 31, 2021 and September 30, 2020, the fair values of cash and cash equivalents, accounts receivable and accounts payable approximate carrying values due to the short maturity of these items. The Company measures the fair value of pension plan assets and liabilities, deferred compensation plan assets and liabilities on a recurring basis pursuant to ASC Topic No. 820, Fair Value Measurement . ASC Topic No. 820 establishes a three‑tier fair value hierarchy, which prioritizes the inputs used in measuring fair value. These tiers include: Level 1: Quoted prices for identical instruments in active markets. Level 2: Quoted prices for similar instruments in active markets; quoted prices for identical or similar instruments in markets that are not active; and model‑derived valuations whose inputs are observable or whose significant value driver is observable. Level 3: Unobservable inputs in which little or no market data is available, therefore requiring an entity to develop its own assumptions. The following table presents the Company’s financial assets and liabilities at fair value. The fair values related to the pension plan assets are determined using net asset value (“NAV”) as a practical expedient, or by information categorized in the fair value hierarchy level based on the inputs used to determine fair value. The reported carrying amounts of deferred compensation plan assets and liabilities and debt approximate their fair values. The Company uses interest rates and other relevant information generated by market transactions involving similar instruments to fair value these assets and liabilities, therefore all are classified as Level 2 within the valuation hierarchy. Net Asset Value Quoted Market Significant Other Significant As of March 31, 2021 Assets: Pension plan Cash $ — $ 655 $ — $ — Global Multi-Asset Fund 14,814 — — — Government Securities 2,293 — — — Liability Driven Investment 5,754 — — — Guernsey Unit Trust 2,241 — — — Global Absolute Return 2,251 — — — Deferred compensation plan assets Cash — 1,340 — — Mutual Funds — 17,790 — — Interest rate swap — — 5,631 — Foreign currency forward contracts — — 49 — Liabilities: Pension plan — — (48,168) — Deferred compensation plan liabilities — — (23,058) — Long‑term debt — — (887,902) — Foreign currency forward contracts — — (166) — Earn-outs related to acquisitions — — — (295) Option and Purchase Right — — — (7,739) As of September 30, 2020 Assets: Pension plan Cash $ — $ 15,061 $ — $ — Government Securities 4,924 — — — Liability Driven Investment 3,604 — — — Guernsey Unit Trust 1,881 — — — Global Absolute Return 2,060 — — — Deferred compensation plan assets Trust Assets — 55 — — Insurance — — 19,804 — Foreign currency forward contracts — — 140 — Liabilities: Pension plan — — (47,389) — Deferred compensation plan liabilities — — (21,439) — Long‑term debt — — (872,441) — Interest rate swap — — (4,669) — Foreign currency forward contracts — — (47) — Earn-outs related to acquisitions — — — (295) Option and Purchase Right — — — (7,739) The pension plan assets and liabilities and deferred compensation plan assets and liabilities are included in Other non‑current assets and Other non‑current liabilities at March 31, 2021 and September 30, 2020.

Accounts Receivable

Accounts Receivable	6 Months Ended
	Mar. 31, 2021
Receivables [Abstract]
Accounts receivable	Accounts Receivable All trade receivables are reported on the Consolidated Balance Sheets at the outstanding principal amount adjusted for any allowance for credit losses and any charge offs. The Company provides an allowance for credit losses to reduce trade receivables to their estimated net realizable value equal to the amount that is expected to be collected. This allowance is estimated based on historical collection experience, the aging of receivables, specific current and expected future macro-economic and market conditions, and assessments of the current creditworthiness and economic status of customers. The Company considers a receivable delinquent if it is unpaid after the term of the related invoice has expired. Write‑offs are recorded at the time all collection efforts have been exhausted. The Company reviews its allowance for credit losses on a quarterly basis. Accounts receivable are summarized as follows: March 31, September 30, Accounts receivable $ 231,227 $ 264,536 Allowance for credit losses (3,884) (4,057) Receivables, net $ 227,343 $ 260,479 The movement in the allowance for credit losses was as follows for the six months ended March 31, 2021: Balance at September 30, 2020 $ (4,057) Charged to costs and expenses (12) Write-offs 209 Foreign currency and other (24) Balance at March 31, 2021 $ (3,884)

Inventories

Inventories	6 Months Ended
	Mar. 31, 2021
Inventory Disclosure [Abstract]
Inventories	Inventories The major classes of Inventories, net are as follows: March 31, September 30, Raw materials and supplies $ 82,065 $ 78,319 Work in progress 19,497 15,654 Finished goods and products held for resale 61,918 56,435 Costs of unbilled projects 4,143 3,438 Reserves for excess and obsolete (10,836) (11,467) Inventories, net $ 156,787 $ 142,379

Property, Plant, and Equipment

Property, Plant, and Equipment	6 Months Ended
	Mar. 31, 2021
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Property, Plant, and Equipment Property, plant, and equipment consists of the following: March 31, September 30, Machinery and equipment $ 376,831 $ 357,650 Rental equipment 236,469 221,953 Land and buildings 69,541 70,245 Construction in process 53,324 48,325 736,165 698,173 Less: accumulated depreciation (364,297) (333,712) $ 371,868 $ 364,461 The Company entered into secured financing agreements that require providing a security interest in specified equipment. As of March 31, 2021 and September 30, 2020, the gross and net amounts of those assets are as follows: March 31, September 30, Gross Net Gross Net Machinery and equipment $ 68,578 $ 55,023 $ 63,305 $ 52,620 Construction in process 15,140 15,140 8,098 8,098 $ 83,718 $ 70,163 $ 71,403 $ 60,718 Depreciation expense and maintenance and repairs expense for the three and six months ended March 31, 2021 and 2020 were as follows: Three Months Ended Six Months Ended 2021 2020 2021 2020 Depreciation expense $ 18,769 $ 18,185 $ 37,280 $ 35,488 Maintenance and repair expense 4,754 5,249 9,962 11,314

Goodwill

Goodwill	6 Months Ended
	Mar. 31, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	Goodwill Changes in the carrying amount of goodwill are as follows: Integrated Solutions and Services Applied Product Technologies Total Balance at September 30, 2020 $ 224,381 $ 172,824 $ 397,205 Business combinations and divestitures 5,988 — 5,988 Measurement period adjustment (3,485) — (3,485) Foreign currency translation 2,565 2,120 4,685 Balance at March 31, 2021 $ 229,449 $ 174,944 $ 404,393 As of March 31, 2021 and September 30, 2020, $155,704 and $153,004, respectively, of goodwill was deductible for tax purposes.

Debt

Debt	6 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
Debt	Debt Long‑term debt consists of the following: March 31, September 30, First Lien Term Loan, due December 20, 2024 (1) $ 814,538 $ 819,276 First Lien Credit Agreement Revolving Credit Facility (1) — — Equipment Financing, due April 30, 2021 to July 5, 2029, interest rates ranging from 3.25% to 8.07% 74,382 63,918 Notes Payable, due July 31, 2023 507 611 Mortgage (2) — 1,665 Total debt 889,427 885,470 Less unamortized deferred financing fees (8,392) (9,436) Total net debt 881,035 876,034 Less current portion (21,343) (14,339) Total long‑term debt $ 859,692 $ 861,695 (1) On April 1, 2021, the Company paid off the outstanding balance of the First Lien Term Loan (as defined below) and entered into the 2021 Credit Agreement (as defined below). See Note 23, “Subsequent Events” for further discussion. (2) In November 2020, the Company paid off the outstanding balance of the mortgage due June 30, 2028. Term Facilities and Revolving Credit Facility On January 15, 2014, EWT III entered into a First Lien Credit Agreement (as modified, amended or supplemented from time to time, the “Credit Agreement”) and a Second Lien Credit Agreement among EWT III, EWT II, the lenders party thereto and Credit Suisse AG as administrative agent and collateral agent. The term loans outstanding under the Second Lien Credit Agreement were prepaid on October 28, 2016. The Credit Agreement also makes available to the Company a revolving credit facility (the “Revolver”) of up to $125,000, with a letter of credit sublimit of up to $45,000. The term loans outstanding under the Credit Agreement (the “First Lien Term Loan”) mature on December 20, 2024, and the Revolver matures on December 20, 2022. The Company makes quarterly principal payments of $2,369. At March 31, 2021, the interest rate on borrowings was 2.61%, comprised of 0.11% LIBOR plus the 2.50% spread. Deferred financing fees related to the First Lien Term Loan were included as a contra liability to debt on the Consolidated Balance Sheets as follows: March 31, September 30, Current portion of deferred financing fees (1) $ (2,147) $ (2,112) Long-term portion of deferred financing fees (2) (6,245) (7,324) Total deferred financing fees $ (8,392) $ (9,436) (1) Included in Current portion of debt, net of deferred financing fees on the Consolidated Balance Sheets. (2) Included in Long-term debt, net of deferred financing fees on the Consolidated Balance Sheets. Amortization of deferred financing fees included in interest expense were $518 and $421 for the three months ended March 31, 2021 and 2020, respectively and $1,044 and $936 for the six months ended March 31, 2021 and 2020, respectively. The following summarizes the Company’s outstanding borrowings under the Revolver and outstanding letters of credit as of March 31, 2021 and September 30, 2020, respectively. March 31, September 30, Borrowing availability under the Revolver $ 125,000 $ 125,000 Outstanding borrowings under the Revolver — — Outstanding letters of credit under the Revolver 11,904 12,963 Unused amounts under the Revolver $ 113,096 $ 112,037 Additional letters of credit under a separate arrangement $ 33 $ 52 The Credit Agreement contains limitations on incremental borrowings, is subject to leverage ratios and allows for optional prepayments. Under certain circumstances, the Company may be required to remit excess cash flows as defined based upon exceeding certain leverage ratios. The Company did not exceed such ratios during the six months ended March 31, 2021, does not anticipate exceeding such ratios during the year ending September 30, 2021, and therefore does not anticipate any additional repayments during the year ending September 30, 2021. Equipment Financings During the six months ended March 31, 2021, the Company completed the following equipment financings: Date Entered Due Fixed Principal Amount March 31, 2021 March 31, 2028 3.85 % $ 3,630 March 31, 2021 April 30, 2021 (1) 3.25 % 2,559 December 31, 2020 April 30, 2021 (1) 3.25 % 3,899 December 30, 2020 December 30, 2027 3.73 % 3,905 $ 13,993 (1) Represents an advance received from the lender in which the Company is making interest only payments. The Company may convert to a term loan financing for eight years at any time through June 30, 2021. Repayment Schedule Aggregate maturities of all long‑term debt, including current portion of long‑term debt and excluding finance lease obligations as of March 31, 2021, are presented below: Fiscal Year Remainder of 2021 $ 14,982 2022 17,293 2023 17,598 2024 797,448 2025 8,081 Thereafter 34,025 Total $ 889,427

Derivative Financial Instrument

Derivative Financial Instruments	6 Months Ended
	Mar. 31, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments and Hedging Activities Disclosure [Text Block]	Derivative Financial Instruments Interest Rate Risk Management The Company is subject to market risk exposure arising from changes in interest rates on the senior secured credit facilities, which bear interest at rates that are indexed against LIBOR. The Company’s objectives in using interest rate derivatives are to add stability to interest expense and to mitigate its exposure to rising interest rates. To accomplish these objectives, on May 22, 2020, the Company entered into an interest rate swap to mitigate risks associated with variable rate debt. The interest rate swap became effective on June 30, 2020, has a term of five years to hedge the variability of interest payments on the first $500,000 of the Company’s senior secured debt and fixes the LIBOR rate on this portion of the senior secured debt at 0.55%. The interest rate swap has been designated as a cash flow hedge and unrealized gains or losses, net of income tax, are recorded as a component of Accumulated Other Comprehensive Income (“AOCI”) on the Consolidated Balance Sheets. As interest payments are made, the realized gain or loss on the payments is recorded in Interest expense on the Unaudited Consolidated Statements of Operations. Foreign Currency Risk Management The Company’s functional currency is the U.S. dollar. By operating internationally, the Company is subject to foreign currency risk from transactions denominated in currencies other than the U.S. dollar (“foreign currencies”). To mitigate cross-currency transaction risk, the Company analyzes significant exposures where it has receipts or payments in a currency other than the functional currency of its operations, and from time to time may strategically enter into short-term foreign currency forward contracts to lock in some or all of the cash flows associated with these transactions. The Company is also subject to currency translation risk associated with converting the foreign operations’ financial statements into U.S. dollars. The Company uses foreign currency derivative contracts in order to manage the effect of exchange fluctuations on forecasted sales and purchases that are denominated in foreign currencies. To mitigate the impact of foreign exchange rate risk, the Company entered into a series of forward contracts designated as cash flow hedges. As of March 31, 2021, the notional amount of the forward contracts held to sell foreign currencies was $8,866. Credit Risk Management The counterparties to the Company’s derivative contracts are highly-rated financial institutions. The Company regularly reviews the creditworthiness of its financial counterparties and fully expects the counterparties to perform under their respective agreements. The Company is not subject to any obligations to post collateral under derivative instrument contracts. The Company records all derivative instruments on a gross basis in the Consolidated Balance Sheets. Accordingly, there are no offsetting amounts that net assets against liabilities. Derivatives Designated as Cash Flow Hedges The Company accounts for derivatives and hedging activities in accordance with ASC Topic No. 815, Derivatives and Hedging (“Topic No. 815”). As required by Topic No. 815, the Company records all derivatives on the balance sheet at fair value and adjusts to market on a quarterly basis. The Company’s interest rate swap is valued based on readily-observable market inputs, such as quotations on interest rates and LIBOR yield curves at the reporting date. The Company’s foreign currency forward contracts are valued based on quoted forward foreign exchange prices and spot rates at the reporting date. For a derivative that is designated as a cash flow hedge, changes in the fair value of the derivative are recognized in AOCI until the hedged item affects earnings. The Company does not use derivative financial instruments for trading or speculative purposes. The following represents the fair value recorded for derivatives designated as cash flow hedges for the periods presented: Asset Derivatives Balance Sheet Location March 31, September 30, Interest rate swap Prepaid and other current assets $ 5,631 $ — Foreign currency forward contracts Prepaid and other current assets 35 133 Liability Derivative Balance Sheet Location March 31, September 30, Interest rate swap Accrued expenses and other current liabilities $ — $ 4,669 Foreign currency forward contracts Accrued expenses and other current liabilities 158 47 The following represents the amount of gain (loss) recognized in AOCI (net of tax) during the periods presented: Three Months Ended Six Months Ended 2021 2020 2021 2020 Interest rate swap $ 8,811 $ — $ 9,268 $ — Interest rate cap — 15 — 1 Foreign currency forward contracts (335) (179) (332) (160) The following represents the amount of (loss) gain on foreign currency forward contracts reclassified from AOCI into earnings during the periods presented: Three Months Ended Six Months Ended Location of (Loss) Gain 2021 2020 2021 2020 Cost of product sales and services $ (13) $ (6) $ (13) $ (6) General and administrative expense (40) (24) (72) $ 30 Selling and marketing expense (39) 28 (39) 28 Interest expense (523) — (1,033) — $ (615) $ (2) $ (1,157) $ 52 Based on the fair value amounts of the Company’s cash flow hedges at March 31, 2021, the Company expects that approximately $113 of pre-tax net losses will be reclassified from AOCI into earnings during the next twelve months. The amount ultimately realized, however, will differ as exchange rates vary and the underlying contracts settle. Derivatives Not Designated as Cash Flow Hedges The following represents the fair value recorded for derivatives not designated as cash flow hedges for the periods presented: Asset Derivatives Balance Sheet Location March 31, September 30, Foreign currency forward contracts Prepaid and other current assets $ 14 $ 7 Liability Derivatives Balance Sheet Location March 31, September 30, Foreign currency forward contracts Accrued expenses and other current liabilities $ 8 $ —

Product Warranties

Product Warranties	6 Months Ended
	Mar. 31, 2021
Guarantees and Product Warranties [Abstract]
Product warranties	Product Warranties A reconciliation of the activity related to the accrued warranty, including both the current and long‑term portions, is as follows: Current Product Warranties Non-Current Product Warranties Six Months Ended Six Months Ended 2021 2020 2021 2020 Balance at beginning of the period $ 6,115 $ 4,922 $ 1,724 $ 2,332 Warranty provision for sales 2,188 1,892 714 62 Settlement of warranty claims (1,699) (2,567) (471) (1,248) Amounts related to sale of the Memcor product line — 795 — 135 Foreign currency translation and other 110 65 22 (120) Balance at end of the period $ 6,714 $ 5,107 $ 1,989 $ 1,161

Restructuring and Related Charg

Restructuring and Related Charges	6 Months Ended
	Mar. 31, 2021
Restructuring and Related Activities [Abstract]
Restructuring and related charges	Restructuring and Related Charges To better align its resources with its growth strategies and reduce its cost structure, the Company commits to various restructuring plans as necessary. The Company has undertaken various restructuring initiatives, including undertaking activities to reduce the cost structure and rationalize location footprint following the sale of the Memcor product line, transitioning from a three-segment structure to a two-segment operating model designed to better serve the needs of customers worldwide, and various initiatives within the Integrated Solutions and Services segment to drive efficiency and effectiveness in certain divisions. The Company currently expects to incur approximately $2,000 to $3,000 of costs through the remainder of fiscal 2021 related to restructuring charges following the sale of the Memcor product line. The Company currently expects to incur approximately $500 to $700 of cash costs through the remainder of fiscal 2021 as a result of its transition to a two-segment operating model related to other non-employee related business optimizations. The Company currently expects to incur approximately $500 to $1,000 of costs through the remainder of fiscal 2021 related to the restructuring within certain divisions of the Integrated Solutions and Services segment. The table below sets forth the amounts accrued for the restructuring components and related activity: Six Months Ended 2021 2020 Balance at beginning of the period $ 970 $ 655 Restructuring charges following the sale of the Memcor product line 3,808 3,659 Restructuring charges related to two-segment realignment 562 1,233 Restructuring charges related to other initiatives 1,444 780 Release of prior reserves (283) (62) Write off charges (966) — Cash payments (4,359) (5,831) Other adjustments 9 — Balance at end of the period $ 1,185 $ 434 The balances for accrued restructuring liabilities at March 31, 2021 and September 30, 2020, are recorded in Accrued expenses and other liabilities on the Consolidated Balance Sheets. Restructuring charges primarily represent severance charges and other employee costs, fixed asset write-offs and certain relocation expenses. The Company expects to pay the remaining amounts accrued as of March 31, 2021 during the remainder of fiscal 2021. The table below sets forth the location of amounts recorded above on the Unaudited Consolidated Statements of Operations: Six Months Ended 2021 2020 Cost of product sales and services $ 3,428 $ 3,765 General and administrative expense 1,089 1,760 Sales and marketing expense 340 62 Research and development expense (16) 23 Other operating expense, net 690 — $ 5,531 $ 5,610

Employee Benefit Plans

Employee Benefit Plans	6 Months Ended
	Mar. 31, 2021
Retirement Benefits [Abstract]
Employee benefit plans	Employee Benefit Plans The Company maintains multiple employee benefit plans. Certain of the Company’s employees in the UK were participants in a Siemens defined benefit plan established for employees of a UK-based operation acquired by Siemens in 2004. The plan was frozen with respect to future service credits for active employees, however the benefit formula recognized future compensation increases. The Company agreed to establish a replacement defined benefit plan, with the assets of the Siemens scheme transferring to the new scheme on April 1, 2015. The Company’s employees in Germany also participate in a defined benefit plan. Assets equaling the plan’s accumulated benefit obligation were transferred to a German defined benefit plan sponsored by the Company upon the acquisition of EWT from Siemens. The German entity also sponsors a defined benefit plan for a small group of employees located in France. The components of net periodic benefit cost for the plans were as follows: Three Months Ended Six Months Ended 2021 2020 2021 2020 Service cost $ 287 $ 259 $ 571 $ 520 Interest cost 80 68 159 136 Expected return on plan assets (87) (29) (174) (59) Amortization of actuarial losses 110 235 374 471 Pension expense for defined benefit plans $ 390 $ 533 $ 930 $ 1,068 The components of pension expense, other than the service cost component which is included in General and administrative expense, are included in the line item Other operating expense in the Unaudited Consolidated Statements of Operations.

Income Taxes

Income Taxes	6 Months Ended
	Mar. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The income tax provision for interim periods is comprised of tax on ordinary income (loss) provided at the most recent projected annual effective tax rate (“PAETR”), adjusted for the tax effect of discrete items. Management estimates the PAETR each quarter based on the forecasted annual pretax income or (loss). The Company is required to reduce deferred tax assets by a valuation allowance if, based on all available evidence, it is considered more likely than not that some portion or all of the benefit of the deferred tax assets will not be realized in future periods. The Company also records the income tax impact of certain discrete, unusual or infrequently occurring items including changes in judgment about valuation allowances and effects of changes in tax laws or rates, in the interim period in which they occur. When a company maintains a valuation allowance in a particular jurisdiction, no net deferred income tax expense or (benefit) will typically be provided. Jurisdictions with projected income that maintain a valuation allowance typically will form part of the PAETR calculation discussed above. However, jurisdictions with a projected loss for the year that maintain a valuation allowance are excluded from the PAETR calculation. Instead, the income tax for these jurisdictions is computed separately. The actual year-to-date income tax expense (benefit) is the product of the most current PAETR and the actual year-to-date pretax income (loss) adjusted for any discrete tax items. The income tax expense (benefit) for a particular quarter, except for the first quarter, is the difference between the year-to-date calculation of income tax expense (benefit) and the year-to-date calculation for the prior quarter. Items unrelated to current period ordinary income or (loss) are recognized entirely in the period identified as a discrete item of tax. Discrete items generally relate to changes in tax laws, adjustments to prior period’s actual liability determined upon filing tax returns, and adjustments to previously recorded reserves for uncertain tax positions, initially recording or fully reversing valuation allowances. The inclusion of discrete items in a particular quarter can cause the actual effective rate for that quarter to vary significantly from the PAETR. Therefore, the actual effective income tax rate for a particular quarter can vary significantly based upon the jurisdictional mix and timing of actual earnings compared to projected annual earnings, permanent items, earnings for those jurisdictions that maintain a valuation allowance, tax associated with jurisdictions excluded from the PAETR calculation and discrete items. Annual Effective Tax Rate The PAETR, which excludes the impact of discrete items, was 14.6% and 4.5% as of the six months ended March 31, 2021 and 2020, respectively. For the six months ended March 31, 2021, the PAETR was lower than the U.S federal statutory rate of 21.0% primarily due to the impact of maintaining a U.S. valuation allowance provided on U.S. deferred tax assets and is higher than the prior year’s rate which included the impact of the sale of the Memcor product line, and the impact on deferred tax liabilities related to indefinite lived intangibles, a portion of which was reversed in relation to the sale of the Memcor product line. The Company continues to maintain a full valuation allowance on U.S. federal and state net deferred tax assets (excluding the tax effects of deferred tax liabilities associated with indefinite lived intangibles) for the period ending March 31, 2021 as a result of pretax losses incurred since the Company’s inception in early 2014. The Company reported positive pre-tax earnings for the first time in 2017 and again in 2020 and is projecting positive pre-tax earnings in 2021, however, the Company generated pre-tax losses in all other years. The Company was in a three-year cumulative loss position at September 30, 2019, but was no longer in a three-year cumulative loss position at September 30, 2020. The Company believes it is prudent to retain a valuation allowance until a more consistent pattern of earnings is established and net operating loss carryforwards begin to be utilized. Current and Prior Period Tax Expense For the three months ended March 31, 2021, the Company recognized income tax expense of $2,701 on pretax income of $7,783. The rate of 34.7% differed from the U.S. statutory rate of 21.0% principally due to the unfavorable impact of discrete items related to an adjustment for prior periods and recording an uncertain tax position related to a tax audit in a foreign jurisdiction which were partially offset by the impact of maintaining a U.S. valuation allowance against U.S. deferred tax assets. For the three months ended March 31, 2020, the Company recognized an income tax benefit of $7 on pretax income of $7,903. The rate of 0.09% differed from the U.S. statutory rate of 21.0% principally due to the gain on the sale of the Memcor product line which did not generate significant tax expense due to the combination of the U.S. valuation allowance and favorable foreign tax regimes, as well as the favorable impact of the reversal of a portion of deferred tax liabilities related to indefinite lived intangibles. For the six months ended March 31, 2021, the Company recognized income tax expense of $3,785 on pretax income of $15,344. The rate of 24.7% differed from the statutory rate of 21.0% principally due to the unfavorable impact of discrete items related to an adjustment for prior periods and recording an uncertain tax position related to a tax audit in a foreign jurisdiction which were partially offset by the impact of maintaining a U.S. valuation allowance against U.S. deferred tax assets. For the six months ended March 31, 2020, the Company recognized income tax expense of $2,596 on pretax income of $64,012. The rate of 4.06% differed from the statutory rate of 21.0% principally due to the gain on the sale of the Memcor product line which did not generate significant tax expense due to the combination of the U.S. valuation allowance and favorable foreign tax regimes, as well as the favorable impact of the reversal of a portion of deferred tax liabilities related to indefinite lived intangibles.

Share-Based Compensation

Share-Based Compensation	6 Months Ended
	Mar. 31, 2021
Share-based Payment Arrangement [Abstract]
Share Based Compensation	Share-Based Compensation The Company designs equity compensation plans to attract and retain employees while also aligning employees’ interests with the interests of the Company’s shareholders. In addition, members of the Company’s Board of Directors (the “Board”) participate in equity compensation plans in connection with their service on the Board. The Company established the Evoqua Water Technologies Corp. Stock Option Plan (the “Stock Option Plan”) shortly after the acquisition date of January 16, 2014 . The plan allows certain management employees and the Board to purchase shares in the Company. Under the Stock Option Plan, the number of shares available for award was 11,083. As of March 31, 2021, there were approximately 2,177 shares available for future grants, however, the Company does not currently intend to make additional grants under the Stock Option Plan. In connection with the IPO, the Board adopted, and the Company’s shareholders approved, the Evoqua Water Technologies Corp. 2017 Equity Incentive Plan (the “Equity Incentive Plan”), under which equity awards may be granted in the form of options, restricted stock, restricted stock units, stock appreciation rights, dividend equivalent rights, share awards and performance-based awards (including performance share units and performance-based restricted stock). Upon adoption of the Equity Incentive Plan, 5,100 shares of common stock of the Company were reserved for issuance thereunder. On February 18, 2020, the Company’s shareholders approved the amendment and restatement of the Equity Incentive Plan in order to increase the number of shares of common stock reserved for issuance thereunder by 5,000 shares and incorporate other changes. As of March 31, 2021, there were approximately 4,990 shares available for grants under the Equity Incentive Plan. Option awards are granted at various times during the year, vest ratably at 25% per year, and are exercisable at the time of vesting. The options granted have a ten A summary of the stock option activity as of March 31, 2021 is presented below: (In thousands, except per share amounts) Options Weighted Average Exercise Price/Share Weighted Average Remaining Contractual Term Aggregate Intrinsic Value Outstanding at September 30, 2020 7,430 $ 10.30 5.9 years $ 83,152 Granted 611 24.76 Exercised (2,185) 6.04 Forfeited (7) 19.20 Outstanding at March 31, 2021 5,849 $ 13.39 6.4 years $ 75,542 Options exercisable at March 31, 2021 3,857 $ 9.62 5.2 years $ 64,333 Options vested and expected to vest at March 31, 2021 5,774 $ 13.25 6.3 years $ 75,349 The total intrinsic value of options exercised (which is the amount by which the stock price exceeded the exercise price of the options on the date of exercise) during the six months ended March 31, 2021 was $43,564. A summary of the status of the Company's non-vested stock options as of and for the six months ended March 31, 2021 is presented below. (In thousands, except per share amounts) Shares Weighted Average Grant Date Fair Value/Share Nonvested at beginning of period 2,166 $ 5.56 Granted 611 8.98 Vested (778) 5.56 Forfeited (7) 6.47 Nonvested at end of period 1,992 $ 6.60 The total fair value of options vested during the six months ended March 31, 2021, was $4,326. Restricted Stock Units The following is a summary of the RSU activity for the six months ended March 31, 2021. (In thousands, except per share amounts) Shares Weighted Average Grant Date Fair Value/Share Outstanding at September 30, 2020 750 $ 17.86 Granted 494 24.69 Vested (234) 17.64 Forfeited (3) 18.85 Cancelled (7) 21.22 Outstanding at March 31, 2021 1,000 $ 21.26 Expected to vest at March 31, 2021 948 $ 21.11 Expense Measurement and Recognition The Company recognizes share-based compensation for all currently outstanding awards and, in future periods, will recognize compensation costs for the unvested portion of awards based on grant date fair values. Total share-based compensation expense was $3,214 and $2,326 during the three months ended March 31, 2021 and 2020, respectively, of which $3,214 and $2,304 was non-cash, respectively. Total share-based compensation expense was $6,290 and $6,017 during the six months ended March 31, 2021 and 2020, respectively, of which $6,233 and $5,984 was non-cash, respectively. The unrecognized compensation expense related to stock options and RSUs was $11,897 and $19,110, respectively at March 31, 2021, and is expected to be recognized over a weighted average period of 2.5 years and 2.6 years, respectively. The Company received $13,430 from the exercise of stock options during the six months ended March 31, 2021. Employee Stock Purchase Plan Effective October 1, 2018, the Company implemented an employee stock purchase plan (the “ESPP”) which allows employees to purchase shares of the Company’s stock at 85% of the lower of the fair market value on the first day of the applicable offering period or on the last business day of a six

Concentration of Credit Risk

Concentration of Credit Risk	6 Months Ended
	Mar. 31, 2021
Risks and Uncertainties [Abstract]
Concentration of credit risk	Concentration of Credit RiskThe Company’s cash and cash equivalents and accounts receivable are potentially subject to concentration of credit risk. Cash and cash equivalents are placed with financial institutions that management believes are of high credit quality. Accounts receivable are derived from revenue earned from customers located in the U.S. and internationally and generally do not require collateral. The Company’s trade receivables do not represent a significant concentration of credit risk at March 31, 2021 and September 30, 2020 due to the wide variety of customers and markets into which products are sold and their dispersion across geographic areas. The Company does perform ongoing credit evaluations of its customers and maintains an allowance for potential credit losses on trade receivables. As of and for the three and six months ended March 31, 2021 and 2020, no customer accounted for more than 10% of net sales or net accounts receivable.The Company operates predominantly in ten countries worldwide and provides a wide range of proven product brands and advanced water and wastewater treatment technologies, mobile and emergency water supply solutions and service contract options through its Integrated Solutions and Services and Applied Product Technologies segments. The Company is a multi-national business but its sales and operations are primarily in the U.S. Sales to unaffiliated customers are based on the Company locations that maintain the customer relationship and transact the external sale.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Mar. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Guarantees From time to time, the Company is required to provide letters of credit, bank guarantees, or surety bonds in support of its commitments and as part of the terms and conditions on water treatment projects. In addition, the Company is required to provide letters of credit or surety bonds to the Department of Environmental Protection or equivalent in some states in order to maintain its licenses to handle toxic substances at certain of its water treatment facilities. These financial instruments typically expire after all Company commitments have been met, a period typically ranging from twelve months to ten years, or more in some circumstances. The letters of credit, bank guarantees, or surety bonds are arranged through major banks or insurance companies. In the case of surety bonds, the Company generally indemnifies the issuer for all costs incurred if a claim is made against the bond. The following summarizes the Company’s outstanding letters of credit and surety bonds as of March 31, 2021 and September 30, 2020, respectively. March 31, September 30, Revolving credit capacity $ 45,000 $ 45,000 Letters of credit outstanding 11,904 12,963 Remaining revolving credit capacity $ 33,096 $ 32,037 Surety capacity $ 250,000 $ 230,000 Surety issuances 147,565 152,990 Remaining surety available $ 102,435 $ 77,010 The longest maturity date of letters of credit and surety bonds in effect as of March 31, 2021 was March 20, 2030. Litigation From time to time, as a normal incident of the nature and kind of business in which the Company is engaged, various claims or charges are asserted and litigation is commenced against it arising from or related to: product liability; personal injury; trademarks, trade secrets or other intellectual property; shareholder disputes; labor and employee disputes; commercial or contractual disputes; breach of warranty; or environmental matters. Claimed amounts may be substantial but may not bear any reasonable relationship to the merits of the claim or the extent of any real risk of court or arbitral awards. While it is not feasible to predict the outcome of these matters with certainty, and some lawsuits, claims or proceedings may be disposed or decided unfavorably, the Company does not expect that any asserted or un-asserted legal claims or proceedings, individually or in the aggregate, will have a material adverse effect on its results of operations, or financial condition.

Accrued Expenses and Other Liab

Accrued Expenses and Other Liabilities	6 Months Ended
	Mar. 31, 2021
Payables and Accruals [Abstract]
Accrued Expenses and Other Liabilities	Accrued Expenses and Other Liabilities Accrued expenses and other liabilities consisted of the following: March 31, September 30, Salaries, wages and other benefits $ 59,245 $ 67,766 Obligation under operating leases 13,119 12,767 Obligation under finance leases 11,869 11,362 Third party commissions 9,192 9,270 Taxes, other than income 3,939 5,316 Insurance liabilities 3,760 3,954 Provisions for litigation 2,072 2,580 Frontier Option liability 1,490 — Severance payments 1,185 970 Earn-outs related to acquisitions 295 295 Fair value of liability derivatives 166 4,716 Other 28,360 24,393 $ 134,692 $ 143,389

Business Segments

Business Segments	6 Months Ended
	Mar. 31, 2021
Segment Reporting [Abstract]
Business segments	Business Segments The Company’s reportable operating segments are defined as components of an enterprise about which separate financial information is available that is evaluated on a regular basis by the chief operating decision maker, or decision making group, in deciding how to allocate resources to an individual segment and in assessing performance. The key factors used to identify these reportable operating segments are the organization and alignment of the Company’s internal operations, the nature of the products and services, and customer type. The Company has two reportable operating segments, Integrated Solutions and Services and Applied Product Technologies. The business segments are described as follows: Integrated Solutions and Services is a group entirely focused on engaging directly with end users through direct sales with a market vertical focus. Integrated Solutions and Services provides tailored services and solutions in collaboration with the customers backed by life‑cycle services including on‑demand water, outsourced water, recycle / reuse and emergency response service alternatives to improve operational reliability, performance and environmental compliance. Key offerings within this segment also include equipment systems for industrial needs (influent water, boiler feed water, ultrahigh purity, process water, wastewater treatment and recycle / reuse), full-scale outsourcing of operations and maintenance, and municipal services, including odor and corrosion control services. Applied Product Technologies is focused on developing product platforms to be sold primarily through third party channels. This segment primarily engages in indirect sales through independent sales representatives, distributors and aftermarket channels. Applied Product Technologies provides a range of highly differentiated and scalable products and technologies specified by global water treatment designers, original equipment manufacturers (“OEMs”), engineering firms and integrators. Key offerings within this segment include filtration and separation, disinfection, wastewater solutions, anode and electrochlorination technology and aquatics technologies and solutions for the global recreational and commercial pool market. Corporate activities include general corporate expenses, elimination of inter-segment transactions, interest income and expense and certain other charges. Certain other charges may include restructuring and other business transformation charges that have been undertaken to align and reposition the Company to the current reporting structure, acquisition related costs (including transaction costs and certain integration costs) and share-based compensation charges. Since certain administrative and other operating expenses and other items have not been allocated to business segments, the results in the below table are not necessarily a measure computed in accordance with generally accepted accounting principles and may not be comparable to other companies. Reportable operating segment revenue and operating profit for the three and six months ended March 31, 2021 and 2020 were as follows: Three Months Ended Six Months Ended 2021 2020 2021 2020 Total revenue Integrated Solutions and Services $ 228,203 $ 240,824 $ 444,956 $ 472,624 Applied Product Technologies 146,107 129,424 269,688 267,953 Total revenue 374,310 370,248 714,644 740,577 Intersegment revenue Integrated Solutions and Services 4,069 2,939 6,105 6,601 Applied Product Technologies 23,677 15,646 39,782 36,208 Total intersegment revenue 27,746 18,585 45,887 42,809 Revenue to external customers Integrated Solutions and Services 224,134 237,885 438,851 466,023 Applied Product Technologies 122,430 113,778 229,906 231,745 Total revenue $ 346,564 $ 351,663 $ 668,757 $ 697,768 Operating profit (loss) Integrated Solutions and Services $ 30,784 $ 36,695 $ 57,141 $ 69,849 Applied Product Technologies 18,103 23,750 31,483 86,892 Corporate (32,709) (39,290) (56,212) (65,894) Total operating profit 16,178 21,155 32,412 90,847 Interest expense (8,395) (13,252) (17,068) (26,835) Income before income taxes 7,783 7,903 15,344 64,012 Income tax (expense) benefit (2,701) 7 (3,785) (2,596) Net income $ 5,082 $ 7,910 $ 11,559 $ 61,416

Earnings per Share

Earnings per Share	6 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Earnings per share	Earnings Per Share The following table sets forth the computation of basic and diluted earnings from continuing operations per common share (in thousands, except per share amounts): Three Months Ended Six Months Ended 2021 2020 2021 2020 Numerator: Numerator for basic and diluted earnings per common share—Net income attributable to Evoqua Water Technologies Corp. $ 5,036 $ 7,812 $ 11,469 $ 60,957 Denominator: Denominator for basic net income per common share—weighted average shares 118,882 116,459 118,882 116,459 Effect of dilutive securities: Share‑based compensation 3,041 4,391 3,393 4,892 Denominator for diluted net income per common share—adjusted weighted average shares 121,923 120,850 122,275 121,351 Basic earnings attributable to Evoqua Water Technologies Corp. per common share $ 0.04 $ 0.07 $ 0.10 $ 0.52 Diluted earnings attributable to Evoqua Water Technologies Corp. per common share $ 0.04 $ 0.06 $ 0.09 $ 0.50

Subsequent Events

Subsequent Events	6 Months Ended
	Mar. 31, 2021
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events 2021 Credit Agreement On April 1, 2021, EWT III entered into a Credit Agreement (the “2021 Credit Agreement”) among EWT III, as borrower, EWT II, as parent guarantor, the lenders from time to time party thereto, JPMorgan Chase Bank, N.A., as administrative agent and collateral agent, and ING Capital, LLC, as sustainability coordinator. The 2021 Credit Agreement provides for a multi-currency senior secured revolving credit facility in an aggregate principal amount not to exceed the U.S. dollar equivalent of $350,000 (the “2021 Revolving Credit Facility”) and a discounted senior secured term loan facility relating to a term loan (the “2021 Term Loan”) in the amount of $475,000 (together with the 2021 Revolving Credit Facility, the “Senior Facilities”). The 2021 Credit Agreement also provides for a letter of credit sub-facility not to exceed $60,000. On April 1, 2021, EWT III borrowed the full amount of $475,000 under the 2021 Term Loan and $105,000 under the 2021 Revolving Credit Facility. The Senior Facilities are guaranteed by EWT II and certain existing and future direct or indirect wholly-owned domestic subsidiaries of EWT III (together with EWT III, collectively, the “Loan Parties”), and collateralized by a first lien on substantially all of the assets of the Loan Parties, with certain exceptions. The 2021 Term Loan matures on April 1, 2028 and requires quarterly principal payments of $1,188. Any amount owed under the 2021 Revolving Credit Facility will become due and payable in full on April 1, 2026. The net proceeds of the Senior Facilities, together with the net proceeds of the Receivables Securitization Program (as defined below) and cash on hand, were used to repay all outstanding indebtedness, in an aggregate principal amount of approximately $814,538, under the Credit Agreement. The proceeds of the 2021 Revolving Credit Facility may also be used to finance or refinance the working capital and capital expenditures needs of EWT III and certain of its subsidiaries and for general corporate purposes. As a result of the refinancing, the Company wrote off approximately $1,333 of deferred financing fees related to the First Lien Term Loan. In addition, the Company incurred approximately $4,985 of fees, of which approximately $1,931 were recorded as deferred financing fees on the Consolidated Balance Sheets and approximately $3,054 were expensed. Receivables Securitization Program On April 1, 2021, Evoqua Finance LLC (“Evoqua Finance”), an indirect wholly-owned subsidiary of the Company, entered into an accounts receivable securitization program (the “Receivables Securitization Program”) consisting of, among other agreements, (i) a Receivables Financing Agreement (the “Receivables Financing Agreement”) among Evoqua Finance, as the borrower, the lenders from time to time party thereto (the “Receivables Financing Lenders”), PNC Bank, National Association (“PNC Bank”), as administrative agent, Evoqua Water Technologies LLC (“EWT LLC”), an indirect wholly-owned subsidiary of the Company, as initial servicer, and PNC Capital Markets LLC (“PNC Markets”), as structuring agent, pursuant to which the lenders have made available to Evoqua Finance a receivables finance facility (the “Securitization Facility”) in an amount up to $150,000 and (ii) a Sale and Contribution Agreement (the “Sale Agreement”) among Evoqua Finance, as purchaser, EWT LLC, as initial servicer and as an originator, and Neptune Benson, Inc., an indirectly wholly-owned subsidiary of the Company, as an originator (together with EWT LLC, the “Originators”). Under the Receivables Securitization Program, the Originators, pursuant to the Sale Agreement, are required to sell substantially all of their trade receivables and certain related rights to payment and obligations of the Originators with respect to such receivables (the “Receivables”) to Evoqua Finance, which, in turn, will obtain loans secured by the Receivables from the Receivables Financing Lenders pursuant to the Receivables Financing Agreement. On April 1, 2021, Evoqua Finance borrowed $142,200 under the Securitization Facility. The Receivables Financing Lenders under the Receivables Securitization Program receive interest at LIBOR or LMIR as selected by Evoqua Finance. The Receivables Securitization Program matures on April 1, 2024. The Company incurred approximately $822 of fees related to the Receivables Securitization Program which were recorded as deferred financing fees on the Consolidated Balance Sheets. Acquisition

Organization, Consolidation and

Organization, Consolidation and Presentation of Financial Statements (Policies)	6 Months Ended
	Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of presentation	Basis of Presentation The accompanying Unaudited Consolidated Financial Statements have been prepared in accordance with accounting principles generally accepted in the U.S. (“GAAP”). All intercompany transactions have been eliminated. Unless otherwise specified, all dollar and share amounts in these notes are referred to in thousands. The interim Unaudited Consolidated Financial Statements have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). Certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such SEC rules. We believe that the disclosures made are adequate to make the information presented not misleading. In our opinion, all adjustments considered necessary for a fair presentation of the financial statements have been included, and all adjustments are of a normal and recurring nature. We consistently applied the accounting policies described in our Annual Report on Form 10-K for the fiscal year ended September 30, 2020, as filed with the SEC on November 20, 2020 (“2020 Annual Report”), in preparing these Unaudited Consolidated Financial Statements, with the exception of accounting standard updates described in Note 2, “Recent Accounting Pronouncements.” These Unaudited Consolidated Financial Statements should be read in conjunction with the audited financial statements and the notes included in our 2020 Annual Report. Certain prior period amounts have been reclassified to conform to the current period presentation.

Accounting Policies (Policies)

Accounting Policies (Policies)	6 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Recent accounting pronouncements	Recent Accounting Pronouncements Accounting Pronouncements Not Yet Adopted In March 2020, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting (“ASU 2020-04”), which was amended by the subsequent issuance in January 2021 of ASU 2021-01, Reference Rate Reform (Topic 848): Scope (“ASU 2021-01”). ASU 2020-04 became effective immediately and expires on December 21, 2022. ASU 2020-04 allows eligible contracts that are modified to be accounted for as a continuation of those contracts, permits companies to preserve their hedging accounting during the transition period and enables companies to make a one-time election to transfer or sell held-to-maturity debt securities that are affected by rate reform. ASU 2021-01 provides optional expedients and exceptions for contracts, hedging relationships and other transactions that reference the London Inter-Bank Offered Rate (“LIBOR”) or another reference rate expected to be discontinued because of reference rate reform, if certain criteria are met. The Company is currently assessing the impact of the adoption of ASU 2020-04 and ASU 2021-01 on the Company’s Unaudited Consolidated Financial Statements and related disclosures. Accounting Pronouncements Recently Adopted The Company adopted ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments on October 1, 2020 (“ASU 2016-13”). ASU 2016-13 requires entities to use a new forward-looking “expected loss” model that reflects expected credit losses, including credit losses related to trade receivables, and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates which generally will result in the earlier recognition of allowances for losses. The Company adopted ASU 2016-13 us ing a modified retrospective approach and determined that there was no cumulative-effect adjustment to its beginning Retained deficit on the Consolidated Balance Sheets. The adoption of this standard did not hav e a material impact on the Company’s Unaudited Consolidated Financial Statements. See Note 7, “Accounts Receivable” for further details and related disclosures. The following accounting pronouncements were adopted by the Company on October 1, 2020, and the adoptions did not have a material impact on the Company’s Unaudited Consolidated Financial Statements or disclosures: Accounting Standards Updates ASU 2020-03, Codification Improvements to Financial Instruments ASU 2018-19, Codification Improvements to Topic 326, Financial Instruments—Credit Losses ASU 2018-18, Collaborative Arrangements (Topic 808) Clarifying the Interaction between Topic 808 and Topic 606 ASU 2018-13, Fair Value Measurement (Subtopic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement

Acquisitions (Tables)

Acquisitions (Tables)	6 Months Ended
	Mar. 31, 2021
Business Combinations [Abstract]
Schedule of Business Acquisitions, by Acquisition	The preliminary opening balance sheet for Ultrapure is summarized as follows: Current assets $ 2,366 Property, plant and equipment 963 Goodwill 2,545 Intangible assets, net 3,751 Other non-current assets 22 Total assets acquired 9,647 Liabilities assumed (904) Net assets acquired $ 8,743

Revenue (Tables)

Revenue (Tables)	6 Months Ended
	Mar. 31, 2021
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	Information regarding the source of revenue: Three Months Ended Six Months Ended 2021 2020 2021 2020 Revenue from contracts with customers recognized under Topic 606 $ 297,919 $ 314,994 $ 583,107 $ 623,596 Other (1) 48,645 36,669 85,650 74,172 Total $ 346,564 $ 351,663 $ 668,757 $ 697,768 (1) Other revenue relates to revenue recognized pursuant to ASU 2016-02, Leases (Topic 842) , mainly attributable to long term rentals. Information regarding revenue disaggregated by source of revenue and segment is as follows: Three Months Ended March 31, 2021 2020 Integrated Solutions and Services Applied Product Technologies Total Integrated Solutions and Services Applied Product Technologies Total Revenue from capital projects $ 52,093 $ 90,296 $ 142,389 $ 66,092 $ 75,214 $ 141,306 Revenue from aftermarket 32,501 27,576 60,077 31,901 32,762 64,663 Revenue from service 139,540 4,558 144,098 139,892 5,802 145,694 Total $ 224,134 $ 122,430 $ 346,564 $ 237,885 $ 113,778 $ 351,663 Six Months Ended March 31, 2021 2020 Integrated Solutions and Services Applied Product Technologies Total Integrated Solutions and Services Applied Product Technologies Total Revenue from capital projects $ 102,719 $ 167,185 $ 269,904 $ 120,712 $ 150,140 $ 270,852 Revenue from aftermarket 59,647 52,930 112,577 61,574 70,103 131,677 Revenue from service 276,485 9,791 286,276 283,737 11,502 295,239 Total $ 438,851 $ 229,906 $ 668,757 $ 466,023 $ 231,745 $ 697,768 Information regarding revenue disaggregated by geographic area is as follows: Three Months Ended Six Months Ended 2021 2020 2021 2020 United States $ 274,681 $ 290,273 $ 538,812 $ 567,990 Europe 31,527 30,381 52,812 56,493 Asia 26,976 12,720 49,581 31,462 Canada 10,636 16,319 21,815 33,882 Australia 2,744 1,970 5,737 7,941 Total $ 346,564 $ 351,663 $ 668,757 $ 697,768
Contract with Customer, Asset and Liability	The tables below provide a roll-forward of contract assets and contract liabilities balances for the periods presented: Six Months Ended Contract assets (a) 2021 2020 Balance at beginning of period $ 80,759 $ 73,467 Recognized in current period 147,593 172,228 Reclassified to accounts receivable (153,964) (166,535) Amounts related to sale of the Memcor product line — 2,710 Foreign currency 413 (621) Balance at end of period $ 74,801 $ 81,249 (a) Excludes receivable balances which are disclosed on the Consolidated Balance Sheets. Six Months Ended Contract Liabilities 2021 2020 Balance at beginning of period $ 26,259 $ 39,051 Recognized in current period 158,452 157,114 Amounts in beginning balance reclassified to revenue (20,703) (37,497) Current period amounts reclassified to revenue (127,684) (124,194) Amounts related to sale of the Memcor product line — (700) Foreign currency 570 (83) Balance at end of period $ 36,894 $ 33,691

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	The following table presents the Company’s financial assets and liabilities at fair value. The fair values related to the pension plan assets are determined using net asset value (“NAV”) as a practical expedient, or by information categorized in the fair value hierarchy level based on the inputs used to determine fair value. The reported carrying amounts of deferred compensation plan assets and liabilities and debt approximate their fair values. The Company uses interest rates and other relevant information generated by market transactions involving similar instruments to fair value these assets and liabilities, therefore all are classified as Level 2 within the valuation hierarchy. Net Asset Value Quoted Market Significant Other Significant As of March 31, 2021 Assets: Pension plan Cash $ — $ 655 $ — $ — Global Multi-Asset Fund 14,814 — — — Government Securities 2,293 — — — Liability Driven Investment 5,754 — — — Guernsey Unit Trust 2,241 — — — Global Absolute Return 2,251 — — — Deferred compensation plan assets Cash — 1,340 — — Mutual Funds — 17,790 — — Interest rate swap — — 5,631 — Foreign currency forward contracts — — 49 — Liabilities: Pension plan — — (48,168) — Deferred compensation plan liabilities — — (23,058) — Long‑term debt — — (887,902) — Foreign currency forward contracts — — (166) — Earn-outs related to acquisitions — — — (295) Option and Purchase Right — — — (7,739) As of September 30, 2020 Assets: Pension plan Cash $ — $ 15,061 $ — $ — Government Securities 4,924 — — — Liability Driven Investment 3,604 — — — Guernsey Unit Trust 1,881 — — — Global Absolute Return 2,060 — — — Deferred compensation plan assets Trust Assets — 55 — — Insurance — — 19,804 — Foreign currency forward contracts — — 140 — Liabilities: Pension plan — — (47,389) — Deferred compensation plan liabilities — — (21,439) — Long‑term debt — — (872,441) — Interest rate swap — — (4,669) — Foreign currency forward contracts — — (47) — Earn-outs related to acquisitions — — — (295) Option and Purchase Right — — — (7,739)

Accounts Receivable (Tables)

Accounts Receivable (Tables)	6 Months Ended
	Mar. 31, 2021
Receivables [Abstract]
Schedule of accounts receivable	Accounts receivable are summarized as follows: March 31, September 30, Accounts receivable $ 231,227 $ 264,536 Allowance for credit losses (3,884) (4,057) Receivables, net $ 227,343 $ 260,479
Accounts Receivable, Allowance for Credit Loss	The movement in the allowance for credit losses was as follows for the six months ended March 31, 2021: Balance at September 30, 2020 $ (4,057) Charged to costs and expenses (12) Write-offs 209 Foreign currency and other (24) Balance at March 31, 2021 $ (3,884)

Inventories (Tables)

Inventories (Tables)	6 Months Ended
	Mar. 31, 2021
Inventory Disclosure [Abstract]
Schedule of Inventory	The major classes of Inventories, net are as follows: March 31, September 30, Raw materials and supplies $ 82,065 $ 78,319 Work in progress 19,497 15,654 Finished goods and products held for resale 61,918 56,435 Costs of unbilled projects 4,143 3,438 Reserves for excess and obsolete (10,836) (11,467) Inventories, net $ 156,787 $ 142,379

Property, Plant, and Equipment

Property, Plant, and Equipment (Tables)	6 Months Ended
	Mar. 31, 2021
Property, Plant and Equipment [Abstract]
Schedule of Property, Plant and Equipment	Property, plant, and equipment consists of the following: March 31, September 30, Machinery and equipment $ 376,831 $ 357,650 Rental equipment 236,469 221,953 Land and buildings 69,541 70,245 Construction in process 53,324 48,325 736,165 698,173 Less: accumulated depreciation (364,297) (333,712) $ 371,868 $ 364,461 Depreciation expense and maintenance and repairs expense for the three and six months ended March 31, 2021 and 2020 were as follows: Three Months Ended Six Months Ended 2021 2020 2021 2020 Depreciation expense $ 18,769 $ 18,185 $ 37,280 $ 35,488 Maintenance and repair expense 4,754 5,249 9,962 11,314
Schedule of Financial Instruments Owned and Pledged as Collateral	March 31, September 30, Gross Net Gross Net Machinery and equipment $ 68,578 $ 55,023 $ 63,305 $ 52,620 Construction in process 15,140 15,140 8,098 8,098 $ 83,718 $ 70,163 $ 71,403 $ 60,718

Goodwill (Tables)

Goodwill (Tables)	6 Months Ended
	Mar. 31, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	Changes in the carrying amount of goodwill are as follows: Integrated Solutions and Services Applied Product Technologies Total Balance at September 30, 2020 $ 224,381 $ 172,824 $ 397,205 Business combinations and divestitures 5,988 — 5,988 Measurement period adjustment (3,485) — (3,485) Foreign currency translation 2,565 2,120 4,685 Balance at March 31, 2021 $ 229,449 $ 174,944 $ 404,393

Debt (Tables)

Debt (Tables)	6 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
Schedule of Long-term Debt Instruments	Long‑term debt consists of the following: March 31, September 30, First Lien Term Loan, due December 20, 2024 (1) $ 814,538 $ 819,276 First Lien Credit Agreement Revolving Credit Facility (1) — — Equipment Financing, due April 30, 2021 to July 5, 2029, interest rates ranging from 3.25% to 8.07% 74,382 63,918 Notes Payable, due July 31, 2023 507 611 Mortgage (2) — 1,665 Total debt 889,427 885,470 Less unamortized deferred financing fees (8,392) (9,436) Total net debt 881,035 876,034 Less current portion (21,343) (14,339) Total long‑term debt $ 859,692 $ 861,695 (1) On April 1, 2021, the Company paid off the outstanding balance of the First Lien Term Loan (as defined below) and entered into the 2021 Credit Agreement (as defined below). See Note 23, “Subsequent Events” for further discussion. (2) In November 2020, the Company paid off the outstanding balance of the mortgage due June 30, 2028. Deferred financing fees related to the First Lien Term Loan were included as a contra liability to debt on the Consolidated Balance Sheets as follows: March 31, September 30, Current portion of deferred financing fees (1) $ (2,147) $ (2,112) Long-term portion of deferred financing fees (2) (6,245) (7,324) Total deferred financing fees $ (8,392) $ (9,436) (1) Included in Current portion of debt, net of deferred financing fees on the Consolidated Balance Sheets. (2) Included in Long-term debt, net of deferred financing fees on the Consolidated Balance Sheets.
Schedule of Line of Credit Facilities	The following summarizes the Company’s outstanding borrowings under the Revolver and outstanding letters of credit as of March 31, 2021 and September 30, 2020, respectively. March 31, September 30, Borrowing availability under the Revolver $ 125,000 $ 125,000 Outstanding borrowings under the Revolver — — Outstanding letters of credit under the Revolver 11,904 12,963 Unused amounts under the Revolver $ 113,096 $ 112,037 Additional letters of credit under a separate arrangement $ 33 $ 52 The following summarizes the Company’s outstanding letters of credit and surety bonds as of March 31, 2021 and September 30, 2020, respectively. March 31, September 30, Revolving credit capacity $ 45,000 $ 45,000 Letters of credit outstanding 11,904 12,963 Remaining revolving credit capacity $ 33,096 $ 32,037 Surety capacity $ 250,000 $ 230,000 Surety issuances 147,565 152,990 Remaining surety available $ 102,435 $ 77,010
Schedule of Aggregate Maturities of Long-term Debt	Aggregate maturities of all long‑term debt, including current portion of long‑term debt and excluding finance lease obligations as of March 31, 2021, are presented below: Fiscal Year Remainder of 2021 $ 14,982 2022 17,293 2023 17,598 2024 797,448 2025 8,081 Thereafter 34,025 Total $ 889,427
Schedule of Equipment Financing	During the six months ended March 31, 2021, the Company completed the following equipment financings: Date Entered Due Fixed Principal Amount March 31, 2021 March 31, 2028 3.85 % $ 3,630 March 31, 2021 April 30, 2021 (1) 3.25 % 2,559 December 31, 2020 April 30, 2021 (1) 3.25 % 3,899 December 30, 2020 December 30, 2027 3.73 % 3,905 $ 13,993

Derivative Financial Instrume_2

Derivative Financial Instruments (Tables)	6 Months Ended
	Mar. 31, 2021
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Schedule of Derivative Instruments, Effect on Other Comprehensive Income (Loss) [Table Text Block]	The following represents the amount of gain (loss) recognized in AOCI (net of tax) during the periods presented: Three Months Ended Six Months Ended 2021 2020 2021 2020 Interest rate swap $ 8,811 $ — $ 9,268 $ — Interest rate cap — 15 — 1 Foreign currency forward contracts (335) (179) (332) (160)
Derivative Instruments, Gain (Loss) [Table Text Block]	The following represents the amount of (loss) gain on foreign currency forward contracts reclassified from AOCI into earnings during the periods presented: Three Months Ended Six Months Ended Location of (Loss) Gain 2021 2020 2021 2020 Cost of product sales and services $ (13) $ (6) $ (13) $ (6) General and administrative expense (40) (24) (72) $ 30 Selling and marketing expense (39) 28 (39) 28 Interest expense (523) — (1,033) — $ (615) $ (2) $ (1,157) $ 52
Designated as Hedging Instrument
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block]	The following represents the fair value recorded for derivatives designated as cash flow hedges for the periods presented: Asset Derivatives Balance Sheet Location March 31, September 30, Interest rate swap Prepaid and other current assets $ 5,631 $ — Foreign currency forward contracts Prepaid and other current assets 35 133 Liability Derivative Balance Sheet Location March 31, September 30, Interest rate swap Accrued expenses and other current liabilities $ — $ 4,669 Foreign currency forward contracts Accrued expenses and other current liabilities 158 47
Not Designated as Hedging Instrument
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block]	The following represents the fair value recorded for derivatives not designated as cash flow hedges for the periods presented: Asset Derivatives Balance Sheet Location March 31, September 30, Foreign currency forward contracts Prepaid and other current assets $ 14 $ 7 Liability Derivatives Balance Sheet Location March 31, September 30, Foreign currency forward contracts Accrued expenses and other current liabilities $ 8 $ —

Product Warranties (Tables)

Product Warranties (Tables)	6 Months Ended
	Mar. 31, 2021
Guarantees and Product Warranties [Abstract]
Schedule of product warranty liability	A reconciliation of the activity related to the accrued warranty, including both the current and long‑term portions, is as follows: Current Product Warranties Non-Current Product Warranties Six Months Ended Six Months Ended 2021 2020 2021 2020 Balance at beginning of the period $ 6,115 $ 4,922 $ 1,724 $ 2,332 Warranty provision for sales 2,188 1,892 714 62 Settlement of warranty claims (1,699) (2,567) (471) (1,248) Amounts related to sale of the Memcor product line — 795 — 135 Foreign currency translation and other 110 65 22 (120) Balance at end of the period $ 6,714 $ 5,107 $ 1,989 $ 1,161

Restructuring and Related Cha_2

Restructuring and Related Charges (Tables)	6 Months Ended
	Mar. 31, 2021
Restructuring and Related Activities [Abstract]
Schedule of restructuring components	Six Months Ended 2021 2020 Balance at beginning of the period $ 970 $ 655 Restructuring charges following the sale of the Memcor product line 3,808 3,659 Restructuring charges related to two-segment realignment 562 1,233 Restructuring charges related to other initiatives 1,444 780 Release of prior reserves (283) (62) Write off charges (966) — Cash payments (4,359) (5,831) Other adjustments 9 — Balance at end of the period $ 1,185 $ 434 The table below sets forth the location of amounts recorded above on the Unaudited Consolidated Statements of Operations: Six Months Ended 2021 2020 Cost of product sales and services $ 3,428 $ 3,765 General and administrative expense 1,089 1,760 Sales and marketing expense 340 62 Research and development expense (16) 23 Other operating expense, net 690 — $ 5,531 $ 5,610

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	6 Months Ended
	Mar. 31, 2021
Retirement Benefits [Abstract]
Schedule of net benefit costs	The components of net periodic benefit cost for the plans were as follows: Three Months Ended Six Months Ended 2021 2020 2021 2020 Service cost $ 287 $ 259 $ 571 $ 520 Interest cost 80 68 159 136 Expected return on plan assets (87) (29) (174) (59) Amortization of actuarial losses 110 235 374 471 Pension expense for defined benefit plans $ 390 $ 533 $ 930 $ 1,068

Share-Based Compensation (Table

Share-Based Compensation (Tables)	6 Months Ended
	Mar. 31, 2021
Share-based Payment Arrangement [Abstract]
Stock options, activity	A summary of the stock option activity as of March 31, 2021 is presented below: (In thousands, except per share amounts) Options Weighted Average Exercise Price/Share Weighted Average Remaining Contractual Term Aggregate Intrinsic Value Outstanding at September 30, 2020 7,430 $ 10.30 5.9 years $ 83,152 Granted 611 24.76 Exercised (2,185) 6.04 Forfeited (7) 19.20 Outstanding at March 31, 2021 5,849 $ 13.39 6.4 years $ 75,542 Options exercisable at March 31, 2021 3,857 $ 9.62 5.2 years $ 64,333 Options vested and expected to vest at March 31, 2021 5,774 $ 13.25 6.3 years $ 75,349
Schedule of Nonvested Share Activity	A summary of the status of the Company's non-vested stock options as of and for the six months ended March 31, 2021 is presented below. (In thousands, except per share amounts) Shares Weighted Average Grant Date Fair Value/Share Nonvested at beginning of period 2,166 $ 5.56 Granted 611 8.98 Vested (778) 5.56 Forfeited (7) 6.47 Nonvested at end of period 1,992 $ 6.60 The total fair value of options vested during the six months ended March 31, 2021, was $4,326.
Schedule of Share-based Compensation, Restricted Stock Units Award Activity	The following is a summary of the RSU activity for the six months ended March 31, 2021. (In thousands, except per share amounts) Shares Weighted Average Grant Date Fair Value/Share Outstanding at September 30, 2020 750 $ 17.86 Granted 494 24.69 Vested (234) 17.64 Forfeited (3) 18.85 Cancelled (7) 21.22 Outstanding at March 31, 2021 1,000 $ 21.26 Expected to vest at March 31, 2021 948 $ 21.11

Commitments and Contingencies (

Commitments and Contingencies (Tables)	6 Months Ended
	Mar. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Schedule of Line of Credit Facilities	The following summarizes the Company’s outstanding borrowings under the Revolver and outstanding letters of credit as of March 31, 2021 and September 30, 2020, respectively. March 31, September 30, Borrowing availability under the Revolver $ 125,000 $ 125,000 Outstanding borrowings under the Revolver — — Outstanding letters of credit under the Revolver 11,904 12,963 Unused amounts under the Revolver $ 113,096 $ 112,037 Additional letters of credit under a separate arrangement $ 33 $ 52 The following summarizes the Company’s outstanding letters of credit and surety bonds as of March 31, 2021 and September 30, 2020, respectively. March 31, September 30, Revolving credit capacity $ 45,000 $ 45,000 Letters of credit outstanding 11,904 12,963 Remaining revolving credit capacity $ 33,096 $ 32,037 Surety capacity $ 250,000 $ 230,000 Surety issuances 147,565 152,990 Remaining surety available $ 102,435 $ 77,010

Accrued Expenses and Other Li_2

Accrued Expenses and Other Liabilities (Tables)	6 Months Ended
	Mar. 31, 2021
Payables and Accruals [Abstract]
Schedule of Accrued Liabilities	Accrued expenses and other liabilities consisted of the following: March 31, September 30, Salaries, wages and other benefits $ 59,245 $ 67,766 Obligation under operating leases 13,119 12,767 Obligation under finance leases 11,869 11,362 Third party commissions 9,192 9,270 Taxes, other than income 3,939 5,316 Insurance liabilities 3,760 3,954 Provisions for litigation 2,072 2,580 Frontier Option liability 1,490 — Severance payments 1,185 970 Earn-outs related to acquisitions 295 295 Fair value of liability derivatives 166 4,716 Other 28,360 24,393 $ 134,692 $ 143,389

Business Segments (Tables)

Business Segments (Tables)	6 Months Ended
	Mar. 31, 2021
Segment Reporting [Abstract]
Schedule of segment reporting information, by segment	Three Months Ended Six Months Ended 2021 2020 2021 2020 Total revenue Integrated Solutions and Services $ 228,203 $ 240,824 $ 444,956 $ 472,624 Applied Product Technologies 146,107 129,424 269,688 267,953 Total revenue 374,310 370,248 714,644 740,577 Intersegment revenue Integrated Solutions and Services 4,069 2,939 6,105 6,601 Applied Product Technologies 23,677 15,646 39,782 36,208 Total intersegment revenue 27,746 18,585 45,887 42,809 Revenue to external customers Integrated Solutions and Services 224,134 237,885 438,851 466,023 Applied Product Technologies 122,430 113,778 229,906 231,745 Total revenue $ 346,564 $ 351,663 $ 668,757 $ 697,768 Operating profit (loss) Integrated Solutions and Services $ 30,784 $ 36,695 $ 57,141 $ 69,849 Applied Product Technologies 18,103 23,750 31,483 86,892 Corporate (32,709) (39,290) (56,212) (65,894) Total operating profit 16,178 21,155 32,412 90,847 Interest expense (8,395) (13,252) (17,068) (26,835) Income before income taxes 7,783 7,903 15,344 64,012 Income tax (expense) benefit (2,701) 7 (3,785) (2,596) Net income $ 5,082 $ 7,910 $ 11,559 $ 61,416

Earnings per Share (Tables)

Earnings per Share (Tables)	6 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Schedule of earnings per share, basic and diluted	The following table sets forth the computation of basic and diluted earnings from continuing operations per common share (in thousands, except per share amounts): Three Months Ended Six Months Ended 2021 2020 2021 2020 Numerator: Numerator for basic and diluted earnings per common share—Net income attributable to Evoqua Water Technologies Corp. $ 5,036 $ 7,812 $ 11,469 $ 60,957 Denominator: Denominator for basic net income per common share—weighted average shares 118,882 116,459 118,882 116,459 Effect of dilutive securities: Share‑based compensation 3,041 4,391 3,393 4,892 Denominator for diluted net income per common share—adjusted weighted average shares 121,923 120,850 122,275 121,351 Basic earnings attributable to Evoqua Water Technologies Corp. per common share $ 0.04 $ 0.07 $ 0.10 $ 0.52 Diluted earnings attributable to Evoqua Water Technologies Corp. per common share $ 0.04 $ 0.06 $ 0.09 $ 0.50

Description of the Company an_2

Description of the Company and Basis of Presentation (Details) shares in Thousands, $ in Thousands	Feb. 11, 2021shares	Dec. 04, 2020shares	Oct. 29, 2018segment	Mar. 31, 2021segment	Mar. 31, 2021USD ($)segment	Mar. 31, 2020USD ($)
Subsidiary, Sale of Stock [Line Items]
Number of reportable segments | segment			3	2	2
Net cash provided by operating activities					$ 63,058	$ 38,837
Net cash provided by financing activities					8,273	$ (108,327)
Reporting Of Tax Remittances For Certain Equity Awards | Classification Error
Subsidiary, Sale of Stock [Line Items]
Classification error, amount					18,669
Reporting Of Tax Remittances For Certain Equity Awards | Understatement
Subsidiary, Sale of Stock [Line Items]
Net cash provided by operating activities					18,669
Reporting Of Tax Remittances For Certain Equity Awards | Overstatement
Subsidiary, Sale of Stock [Line Items]
Net cash provided by financing activities					18,669
Reporting Of Tax Remittances For Certain Equity Awards | Revision of Prior Period, Error Correction, Adjustment
Subsidiary, Sale of Stock [Line Items]
Classification error, amount					$ 16,854
Additional Secondary Public Offering [Member]
Subsidiary, Sale of Stock [Line Items]
Number of shares issued in transaction (in shares) | shares	16,383	12,000

Investments, Equity Method and

Investments, Equity Method and Joint Ventures (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Apr. 08, 2021	Feb. 28, 2021	Sep. 30, 2020	Oct. 01, 2019
Schedule of Equity Method Investments [Line Items]
Obligation to absorb risk of loss, percentage of partner's equity	100.00%		100.00%
Current assets	$ 717,132		$ 717,132				$ 695,712
Property, plant, and equipment, net	371,868		371,868				364,461
Goodwill	404,393		404,393				397,205
Other non‑current assets	37,836		37,836				27,509
Liabilities	(1,354,914)		(1,354,914)				(1,362,395)
Operating Expenses	(90,151)	$ (99,295)	(169,485)	$ (186,763)
Operating profit (loss)	16,178	21,155	32,412	90,847
Open Option Contracts Written, at Fair Value	(1,490)		(1,490)				0
Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring
Schedule of Equity Method Investments [Line Items]
Open Option Contracts Written, at Fair Value	(7,739)		(7,739)				(7,739)
Other Current Liabilities | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring
Schedule of Equity Method Investments [Line Items]
Open Option Contracts Written, at Fair Value	$ 1,490		$ 1,490				0
Frontier
Schedule of Equity Method Investments [Line Items]
Percentage of voting interests acquired	8.00%		8.00%					60.00%
Remaining percentage to be acquired								40.00%
Frontier | Subsequent Event
Schedule of Equity Method Investments [Line Items]
Percentage of voting interests acquired					68.00%
Frontier | Maximum
Schedule of Equity Method Investments [Line Items]
Remaining percentage to be acquired						10.00%
Treated Water Outsourcing [Member]
Schedule of Equity Method Investments [Line Items]
Partnership interest			50.00%
Current assets	$ 3,462		$ 3,462				4,016
Property, plant, and equipment, net	1,024		1,024				1,145
Goodwill	2,206		2,206				2,206
Liabilities	(1,168)		(1,168)				(1,324)
Cash	1,552		1,552				2,088
Revenues	834	1,210	1,668	3,852
Operating Expenses	(732)	(1,086)	(1,469)	(3,044)
Operating profit (loss)	102	124	199	808
Frontier
Schedule of Equity Method Investments [Line Items]
Current assets	5,045		5,045				4,024
Property, plant, and equipment, net	3,094		3,094				3,159
Goodwill	1,798		1,798				1,798
Other non‑current assets	9,092		9,092				9,918
Liabilities	(5,095)		(5,095)				(3,692)
Cash	1,182		1,182				$ 1,675
Revenues	2,078	1,078	2,848	2,723
Operating Expenses	(2,401)	(2,364)	(4,139)	(4,301)
Operating profit (loss)	$ (323)	$ (1,286)	$ (1,291)	$ (1,578)

Acquisitions (Details)

Acquisitions (Details) - USD ($) $ in Thousands	Mar. 01, 2021	Mar. 31, 2021	Mar. 31, 2020
Business Acquisition [Line Items]
Proceeds from divestiture of business	$ 897		$ 118,894
Loss on divestiture		$ 191	$ (68,051)
Ultrapure
Business Acquisition [Line Items]
Acquisition costs		229
Cash paid at closing		$ 8,743

Acquisitions Opening Balance Sh

Acquisitions Opening Balance Sheet (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Sep. 30, 2020
Business Acquisition [Line Items]
Goodwill	$ 404,393	$ 397,205
Ultrapure
Business Acquisition [Line Items]
Current assets	2,366
Property, plant and equipment	963
Goodwill	2,545
Intangible assets	3,751
Other non-current assets	22
Total assets acquired	9,647
Total liabilities assumed	(904)
Net assets acquired	$ 8,743

Revenue (Details)

Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from product sales and services	$ 346,564	$ 351,663	$ 668,757	$ 697,768
Minimum | Transferred at Point in Time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from product sales and services	$ 100

Revenue (Performance Obligation

Revenue (Performance Obligation) (Details) $ in Thousands	Mar. 31, 2021USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 207,439
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period: 2021-01-01 | Minimum
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period: 2021-01-01 | Maximum
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	24 months

Revenue (Disaggregation of Reve

Revenue (Disaggregation of Revenue) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Revenue from product sales and services		$ 346,564	$ 351,663	$ 668,757	$ 697,768
Operating Leases, Income Statement, Lease Revenue	[1]	48,645	36,669	85,650	74,172
United States
Disaggregation of Revenue [Line Items]
Revenue from product sales and services		274,681	290,273	538,812	567,990
Europe
Disaggregation of Revenue [Line Items]
Revenue from product sales and services		31,527	30,381	52,812	56,493
Asia
Disaggregation of Revenue [Line Items]
Revenue from product sales and services		26,976	12,720	49,581	31,462
Canada
Disaggregation of Revenue [Line Items]
Revenue from product sales and services		10,636	16,319	21,815	33,882
Australia
Disaggregation of Revenue [Line Items]
Revenue from product sales and services		2,744	1,970	5,737	7,941
Integrated Solutions and Services
Disaggregation of Revenue [Line Items]
Revenue from product sales and services		224,134	237,885	438,851	466,023
Applied Product Technologies
Disaggregation of Revenue [Line Items]
Revenue from product sales and services		122,430	113,778	229,906	231,745
Revenue from aftermarket
Disaggregation of Revenue [Line Items]
Revenue from product sales and services		60,077	64,663	112,577	131,677
Revenue from aftermarket | Integrated Solutions and Services
Disaggregation of Revenue [Line Items]
Revenue from product sales and services		32,501	31,901	59,647	61,574
Revenue from aftermarket | Applied Product Technologies
Disaggregation of Revenue [Line Items]
Revenue from product sales and services		27,576	32,762	52,930	70,103
Revenue from service
Disaggregation of Revenue [Line Items]
Revenue from product sales and services		144,098	145,694	286,276	295,239
Revenue from service | Integrated Solutions and Services
Disaggregation of Revenue [Line Items]
Revenue from product sales and services		139,540	139,892	276,485	283,737
Revenue from service | Applied Product Technologies
Disaggregation of Revenue [Line Items]
Revenue from product sales and services		4,558	5,802	9,791	11,502
Revenue from capital projects
Disaggregation of Revenue [Line Items]
Revenue from product sales and services		142,389	141,306	269,904	270,852
Revenue from capital projects | Integrated Solutions and Services
Disaggregation of Revenue [Line Items]
Revenue from product sales and services		52,093	66,092	102,719	120,712
Revenue from capital projects | Applied Product Technologies
Disaggregation of Revenue [Line Items]
Revenue from product sales and services		90,296	75,214	167,185	150,140
Accounting Standards Update 2014-09 [Member]
Disaggregation of Revenue [Line Items]
Revenue from product sales and services		$ 297,919	$ 314,994	$ 583,107	$ 623,596
[1]	Other revenue relates to revenue recognized pursuant to ASU 2016-02, Leases (Topic 842) , mainly attributable to long term rentals.

Revenue (Contract Assets and Li

Revenue (Contract Assets and Liabilities) (Details) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2020	Sep. 30, 2019
Revenue from Contract with Customer [Abstract]
Contract liabilities	$ 36,894	$ 33,691	$ 26,259	$ 39,051
Change in Contract with Customer, Asset [Roll Forward]
beginning of period	80,759	73,467
Recognized in current period	147,593	172,228
Reclassified to accounts receivable	153,964	166,535
Amounts related to sale of the Memcor product line	0	2,710
Foreign currency	413	(621)
end of period	74,801	81,249
Change in Contract with Customer, Liability [Roll Forward]
Recognized in current period	158,452	157,114
Amounts in beginning balance reclassified to revenue	(20,703)	(37,497)
Current period amounts reclassified to revenue	(127,684)	(124,194)
Amounts related to sale of the Memcor product line	0	(700)
Foreign currency	$ 570	$ (83)

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Sep. 30, 2020
Assets:
Mutual Funds	$ 17,790
Liabilities:
Option and purchase right	(1,490)	$ 0
Fair Value, Measurements, Recurring | Quoted Market Prices in Active Markets (Level 1)
Assets:
Cash	1,340
Deferred compensation plan assets
Cash		55
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Assets:
Foreign currency forward contracts	49	140
Deferred compensation plan assets
Mutual Funds		19,804
Liabilities:
Pension plan	(48,168)	(47,389)
Deferred compensation plan liabilities	(23,058)	(21,439)
Long‑term debt	(887,902)	(872,441)
Interest Rate Derivative Liabilities, at Fair Value		(4,669)
Foreign currency forward contracts	(166)	(47)
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Other Current Liabilities | Designated as Hedging Instrument
Deferred compensation plan assets
Interest rate cap	5,631	0
Liabilities:
Interest Rate Derivative Liabilities, at Fair Value	0	(4,669)
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3
Liabilities:
Earn-outs related to acquisitions	(295)	(295)
Option and purchase right	(7,739)	(7,739)
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Other Current Liabilities
Liabilities:
Earn-outs related to acquisitions	(295)	(295)
Option and purchase right	1,490	0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Other Noncurrent Liabilities
Liabilities:
Option and purchase right	6,249	7,739
Fair Value, Measurements, Recurring | Cash | Quoted Market Prices in Active Markets (Level 1)
Assets:
Defined benefit plan, fair value of plan assets	655	15,061
Fair Value, Measurements, Recurring | US Government Agencies Debt Securities
Assets:
Plan assets at net asset value	2,293	4,924
Fair Value, Measurements, Recurring | Liability Driven Investment
Assets:
Plan assets at net asset value	5,754	3,604
Fair Value, Measurements, Recurring | Guernsey Unit Trust
Assets:
Plan assets at net asset value	2,241	1,881
Fair Value, Measurements, Recurring | Global Absolute Return
Assets:
Plan assets at net asset value	2,251	$ 2,060
Fair Value, Measurements, Recurring | Hedge Funds, Multi-strategy
Assets:
Plan assets at net asset value	$ 14,814

Fair Value Measurements (Narrat

Fair Value Measurements (Narrative) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Sep. 30, 2020	Oct. 01, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Option and purchase right	$ 1,490	$ 0
Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Option and purchase right	7,739	7,739
Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring | Other Current Liabilities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Option and purchase right	(1,490)	0
Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring | Other Noncurrent Liabilities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Option and purchase right	$ (6,249)	$ (7,739)
Frontier
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Remaining percentage to be acquired			40.00%
Percentage of voting interests acquired	8.00%		60.00%

Accounts Receivable (Details)

Accounts Receivable (Details) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2021	Sep. 30, 2020
Receivables [Abstract]
Accounts receivable	$ 231,227	$ 264,536
Allowance for credit losses	(3,884)	(4,057)
Accounts receivable, net	227,343	$ 260,479
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at September 30, 2020	(4,057)
Charged to costs and expenses	(12)
Write-offs	209
Foreign currency and other	(24)
Balance at December 31, 2020	$ (3,884)

Inventories (Details)

Inventories (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Sep. 30, 2020
Inventory Disclosure [Abstract]
Raw materials and supplies	$ 82,065	$ 78,319
Work in progress	19,497	15,654
Finished goods and products held for resale	61,918	56,435
Costs of unbilled projects	4,143	3,438
Reserves for excess and obsolete	(10,836)	(11,467)
Inventory, Net	$ 156,787	$ 142,379

Property, Plant, and Equipmen_2

Property, Plant, and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2020
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 736,165		$ 736,165		$ 698,173
Less: accumulated depreciation	(364,297)		(364,297)		(333,712)
Property, plant, and equipment, net	371,868		371,868		364,461
Depreciation and amortization	18,769	$ 18,185	37,280	$ 35,488
Maintenance and repair expense	4,754	$ 5,249	9,962	$ 11,314
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	376,831		376,831		357,650
Land and buildings
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	69,541		69,541		70,245
Construction in process
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	53,324		53,324		48,325
Rental equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 236,469		$ 236,469		$ 221,953

Property, Plant, and Equipmen_3

Property, Plant, and Equipment Property, Plant and Equipment (Secured Financing Agreements) (Details) - Equipment Financings - USD ($) $ in Thousands	Mar. 31, 2021	Sep. 30, 2020
Property, plant and equipment gross [Member]
Debt Instrument [Line Items]
Pledged Assets, Not Separately Reported, Other	$ 83,718	$ 71,403
Property, plant and equipment gross [Member] | Machinery and equipment
Debt Instrument [Line Items]
Pledged Assets, Not Separately Reported, Other	68,578	63,305
Property, plant and equipment gross [Member] | Construction in process
Debt Instrument [Line Items]
Pledged Assets, Not Separately Reported, Other	15,140	8,098
Property, plant and equipment net [Member]
Debt Instrument [Line Items]
Pledged Assets, Not Separately Reported, Other	70,163	60,718
Property, plant and equipment net [Member] | Machinery and equipment
Debt Instrument [Line Items]
Pledged Assets, Not Separately Reported, Other	55,023	52,620
Property, plant and equipment net [Member] | Construction in process
Debt Instrument [Line Items]
Pledged Assets, Not Separately Reported, Other	$ 15,140	$ 8,098

Goodwill (Details)

Goodwill (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Sep. 30, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Business acquisition, goodwill, expected tax deductible, amount	$ 155,704	$ 153,004

Goodwill (Schedule of Goodwill)

Goodwill (Schedule of Goodwill) (Details) $ in Thousands	6 Months Ended
	Mar. 31, 2021USD ($)
Goodwill [Roll Forward]
Goodwill, beginning of the period	$ 397,205
Business combinations and divestitures	5,988
Measurement period adjustment	(3,485)
Foreign currency translation	4,685
Goodwill, end of the period	404,393
Operating Segments | Integrated Solutions and Services
Goodwill [Roll Forward]
Goodwill, beginning of the period	224,381
Business combinations and divestitures	5,988
Measurement period adjustment	(3,485)
Foreign currency translation	2,565
Goodwill, end of the period	229,449
Operating Segments | Applied Product Technologies
Goodwill [Roll Forward]
Goodwill, beginning of the period	172,824
Measurement period adjustment	0
Foreign currency translation	2,120
Goodwill, end of the period	174,944
Goodwill, Written off Related to Sale of Business Unit	$ 0

Debt (Term Facility and Revolvi

Debt (Term Facility and Revolving Credit Facility) (Details) - USD ($) $ in Thousands		3 Months Ended			6 Months Ended
		Mar. 31, 2021		Mar. 31, 2020	Mar. 31, 2021		Mar. 31, 2020	Sep. 30, 2020
Line of Credit Facility [Line Items]
Unamortized discount (premium) and debt issuance costs, net		$ 8,392			$ 8,392			$ 9,436
Total debt		889,427			889,427			885,470
Amortization of debt issuance costs and discounts		518		$ 421	1,044		$ 936
Line of credit facility, remaining borrowing capacity		45,000			45,000			45,000
Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of credit facility, remaining borrowing capacity		125,000			125,000			125,000
First Lien Term Facility, due December 20, 2024
Line of Credit Facility [Line Items]
Unamortized discount (premium) and debt issuance costs, net		(8,392)			(8,392)			(9,436)
First Lien Term Facility, due December 20, 2024 | Other Current Liabilities
Line of Credit Facility [Line Items]
Unamortized discount (premium) and debt issuance costs, net	[1]	(2,147)			(2,147)			(2,112)
First Lien Term Facility, due December 20, 2024 | Other Noncurrent Liabilities
Line of Credit Facility [Line Items]
Unamortized discount (premium) and debt issuance costs, net	[2]	$ (6,245)			$ (6,245)			(7,324)
First Lien Term Facility, due December 20, 2024 | Term Loan
Line of Credit Facility [Line Items]
Debt instrument, interest rate, stated percentage		2.61%			2.61%
Debt instrument, periodic payment, principal					$ 2,369
London Interbank Offered Rate (LIBOR) | First Lien Term Facility, due December 20, 2024 | Term Loan
Line of Credit Facility [Line Items]
Debt instrument, interest rate, stated percentage		2.50%			2.50%
Debt instrument, basis spread on variable rate					0.11%
Revolving Credit Facility
Line of Credit Facility [Line Items]
Total debt		$ 0	[3]		$ 0	[3]		0
First Lien Term Facility, due December 20, 2024
Line of Credit Facility [Line Items]
Total debt		$ 814,538			$ 814,538			$ 819,276
[1]	Included in Current portion of debt, net of deferred financing fees on the Consolidated Balance Sheets.
[2]	Included in Long-term debt, net of deferred financing fees on the Consolidated Balance Sheets.
[3]	On April 1, 2021, the Company paid off the outstanding balance of the First Lien Term Loan (as defined below) and entered into the 2021 Credit Agreement (as defined below). See Note 23, “Subsequent Events” for further discussion.

Debt (Schedule of Long-term Deb

Debt (Schedule of Long-term Debt) (Details) - USD ($) $ in Thousands	Mar. 31, 2021		Dec. 31, 2020	Dec. 30, 2020	Sep. 30, 2020
Debt Instrument [Line Items]
Total debt	$ 889,427				$ 885,470
Less unamortized deferred financing fees	(8,392)				(9,436)
Total net debt	881,035				876,034
Current portion of debt	(21,343)				(14,339)
Total long‑term debt	859,692				861,695
First Lien Term Facility, due December 20, 2024
Debt Instrument [Line Items]
Total debt	814,538				819,276
Revolving Credit Facility
Debt Instrument [Line Items]
Total debt	0	[1]			0
Notes Payable, due July 31, 2023
Debt Instrument [Line Items]
Total debt	507				611
Equipment Financings | Equipment Financing, due April 30, 2021 to July 5, 2029, interest rates ranging from 3.25% to 8.07%
Debt Instrument [Line Items]
Total debt	74,382				63,918
December 31 Equipment Financing [Member] | Equipment Financing, due April 30, 2021 to July 5, 2029, interest rates ranging from 3.25% to 8.07%
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage			0.0325%
Dec 30 Equipment Financing [Member] | Equipment Financing, due April 30, 2021 to July 5, 2029, interest rates ranging from 3.25% to 8.07%
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage				0.0373%
MAGENTO | Facility Financing | Mortgage (2)
Debt Instrument [Line Items]
Total debt	$ 0	[2]			$ 1,665
Minimum | Equipment Financings | Equipment Financing, due April 30, 2021 to July 5, 2029, interest rates ranging from 3.25% to 8.07%
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	3.25%
Maximum | Equipment Financings | Equipment Financing, due April 30, 2021 to July 5, 2029, interest rates ranging from 3.25% to 8.07%
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	8.07%
[1]	On April 1, 2021, the Company paid off the outstanding balance of the First Lien Term Loan (as defined below) and entered into the 2021 Credit Agreement (as defined below). See Note 23, “Subsequent Events” for further discussion.
[2]	In November 2020, the Company paid off the outstanding balance of the mortgage due June 30, 2028.

Debt (Schedule of Line of Credi

Debt (Schedule of Line of Credit Facilities) (Details) - USD ($) $ in Thousands	Mar. 31, 2021		Sep. 30, 2020
Line of Credit Facility [Line Items]
Line of credit facility, remaining borrowing capacity	$ 45,000		$ 45,000
Total debt	889,427		885,470
Debt instrument, unused borrowing capacity, amount	33,096		32,037
Letter of Credit
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount	11,904		12,963
Debt instrument, unused borrowing capacity, amount	113,096		112,037
Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of credit facility, remaining borrowing capacity	125,000		125,000
Line of Credit | Letter of Credit
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount	33		52
Revolving Credit Facility
Line of Credit Facility [Line Items]
Total debt	$ 0	[1]	$ 0
[1]	On April 1, 2021, the Company paid off the outstanding balance of the First Lien Term Loan (as defined below) and entered into the 2021 Credit Agreement (as defined below). See Note 23, “Subsequent Events” for further discussion.

Debt (Long-term Debt Maturities

Debt (Long-term Debt Maturities) (Details) $ in Thousands	Mar. 31, 2021USD ($)
Debt Disclosure [Abstract]
Remainder of 2020	$ 14,982
2021	17,293
2022	17,598
2023	797,448
2024	8,081
Thereafter	34,025
Long-term Debt	$ 889,427

Debt (Schedule of Equipment Fin

Debt (Schedule of Equipment Financings) (Details) - Loans Payable - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Dec. 30, 2020
Equipment Financing Due March 31 2028
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	0.0385%
Total debt	$ 3,630
2021 Equipment Financing Due April 30 2021
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	0.0325%
Total debt	$ 2,559
2020 Equipment Financing Due April 30, 2021
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage		0.0325%
Total debt		$ 3,899
Equipment Financing Due December, 2027
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage			0.0373%
Total debt			$ 3,905
Equipment Financings
Debt Instrument [Line Items]
Total debt	$ 13,993

Derivative Financial Instrume_3

Derivative Financial Instruments (Details) - USD ($) $ in Thousands	May 22, 2020	Mar. 31, 2021
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassification from Accumulated OCI to Income, Estimated Net Amount to be Transferred		$ (113)
Description of Reclassification of Cash Flow Hedge Gain (Loss)		twelve months
Foreign Exchange Forward
Derivative [Line Items]
Derivative, Notional Amount		$ 8,866
Designated as Hedging Instrument | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Term of Contract	5 years
Derivative, Notional Amount	$ 500,000
Derivative, Fixed Interest Rate	0.55%

Derivative Financial Instrume_4

Derivative Financial Instruments (Fair Values) (Details) - Fair Value, Inputs, Level 2 - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Mar. 31, 2021	Sep. 30, 2020
Derivatives, Fair Value [Line Items]
Interest Rate Derivative Liabilities, at Fair Value		$ 4,669
Designated as Hedging Instrument | Other Current Liabilities
Derivatives, Fair Value [Line Items]
Interest Rate Derivative Liabilities, at Fair Value	$ 0	4,669
Foreign Currency Cash Flow Hedge Liability at Fair Value	158	47
Interest rate cap	5,631	0
Designated as Hedging Instrument | Prepaid Expenses and Other Current Assets
Derivatives, Fair Value [Line Items]
Foreign Currency Cash Flow Hedge Asset at Fair Value	$ 35	$ 133

Derivative Financial Instrume_5

Derivative Financial Instruments (Amounts Recognized in AOCI) (Details) - Other Comprehensive Income (Loss) - Designated as Hedging Instrument - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Interest Rate Swap [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	$ 8,811	$ 0	$ 9,268	$ 0
Interest Rate Cap
Derivative Instruments, Gain (Loss) [Line Items]
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	0	15	0	1
Foreign Exchange Forward
Derivative Instruments, Gain (Loss) [Line Items]
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	$ (335)	$ (179)	$ (332)	$ (160)

Derivative Financial Instrume_6

Derivative Financial Instruments (Derivatives Not Designated as Cash Flow Hedges) (Details) - Fair Value, Inputs, Level 2 - Fair Value, Measurements, Recurring - Not Designated as Hedging Instrument - USD ($) $ in Thousands	Mar. 31, 2021	Sep. 30, 2020
Prepaid Expenses and Other Current Assets
Derivatives, Fair Value [Line Items]
Foreign Currency Cash Flow Hedge Liability at Fair Value	$ 14	$ 7
Other Current Liabilities
Derivatives, Fair Value [Line Items]
Foreign Currency Cash Flow Hedge Liability at Fair Value	$ 8	$ 0

Derivative Financial Instrume_7

Derivative Financial Instruments (Amounts Reclassified out of AOCI) (Details) - Reclassification out of Accumulated Other Comprehensive Income [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Foreign Currency Cash Flow Hedge Gain (Loss) Reclassified to Earnings, Net	$ (615)	$ (2)	$ (1,157)	$ 52
Cost of Product Sales and Services
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Foreign Currency Cash Flow Hedge Gain (Loss) Reclassified to Earnings, Net	(13)	(6)	(13)	(6)
General and Administrative Expense
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Foreign Currency Cash Flow Hedge Gain (Loss) Reclassified to Earnings, Net	(40)	(24)	(72)	30
Sales and Marketing Expense
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Foreign Currency Cash Flow Hedge Gain (Loss) Reclassified to Earnings, Net	(39)	28	(39)	28
Interest Expense [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Foreign Currency Cash Flow Hedge Gain (Loss) Reclassified to Earnings, Net	$ (523)	$ 0	$ (1,033)	$ 0

Product Warranties (Details)

Product Warranties (Details) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Movement in Standard and Extended Product Warranty Accrual, Increase (Decrease) [Roll Forward]
Balance at beginning of the period	$ 6,115
Balance at beginning of the period	1,724
Balance at end of the period	6,714
Balance at end of the period	1,989
Other Current Liabilities
Movement in Standard and Extended Product Warranty Accrual, Increase (Decrease) [Roll Forward]
Balance at beginning of the period	6,115	$ 4,922
Warranty provision for sales	2,188	1,892
Settlement of warranty claims	(1,699)	(2,567)
Amounts related to sale of the Memcor product line	0	(795)
Foreign currency translation and other	110	65
Balance at end of the period	6,714	5,107
Other Noncurrent Liabilities
Movement in Standard and Extended Product Warranty Accrual, Increase (Decrease) [Roll Forward]
Balance at beginning of the period	1,724	2,332
Warranty provision for sales	714	62
Settlement of warranty claims	(471)	(1,248)
Amounts related to sale of the Memcor product line	0	(135)
Foreign currency translation and other	22	(120)
Balance at end of the period	$ 1,989	$ 1,161

Restructuring and Related Cha_3

Restructuring and Related Charges (Details) $ in Thousands	Oct. 29, 2018segment	Mar. 31, 2021USD ($)segment	Mar. 31, 2021USD ($)segment	Mar. 31, 2020USD ($)
Restructuring Cost and Reserve [Line Items]
Number of reportable segments | segment	3	2	2
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning of the period			$ 970	$ 655
Restructuring charges			5,531	5,610
Cash payments			(4,359)	(5,831)
Restructuring Reserve, Translation and Other Adjustment			9	0
Other adjustments			283	62
Restructuring reserve, end of the period		$ 1,185	1,185	434
Write off charges			(966)	0
Cost of Product Sales and Services
Restructuring Reserve [Roll Forward]
Restructuring charges			3,428	3,765
General and Administrative Expense
Restructuring Reserve [Roll Forward]
Restructuring charges			1,089	1,760
Sales and Marketing Expense
Restructuring Reserve [Roll Forward]
Restructuring charges			340	62
Research and Development Expense
Restructuring Reserve [Roll Forward]
Restructuring charges			(16)	23
Other Operating Income (Expense)
Restructuring Reserve [Roll Forward]
Restructuring charges			690	0
Two-segment realignment
Restructuring Reserve [Roll Forward]
Restructuring charges			562	1,233
Post Memcor product line sale restructuring [Member]
Restructuring Reserve [Roll Forward]
Restructuring charges			3,808	3,659
Other Restructuring [Member]
Restructuring Reserve [Roll Forward]
Restructuring charges			1,444	$ 780
Other Restructuring [Member] | Two-segment realignment | Maximum
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, expected cost		700	700
Other Restructuring [Member] | Two-segment realignment | Minimum
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, expected cost		500	500
Other Restructuring [Member] | Post Memcor product line sale restructuring [Member] | Maximum
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, expected cost		3,000	3,000
Other Restructuring [Member] | Post Memcor product line sale restructuring [Member] | Minimum
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, expected cost		2,000	2,000
Other Restructuring [Member] | ISS restructuring [Member] | Maximum
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, expected cost		1,000	1,000
Other Restructuring [Member] | ISS restructuring [Member] | Minimum
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, expected cost		$ 500	$ 500

Employee Benefit Plans (Details

Employee Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Retirement Benefits [Abstract]
Service cost	$ 287	$ 259	$ 571	$ 520
Interest cost	80	68	159	136
Expected return on plan assets	(87)	(29)	(174)	(59)
Amortization of actuarial losses	110	235	374	471
Pension expense for defined benefit plans	$ 390	$ 533	$ 930	$ 1,068

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Income Tax Disclosure [Abstract]
Estimated Annual Effective Tax Rate Used to Calculate Income Tax Expense (Benefit)			14.60%	4.50%
Federal statutory income tax rate, percent			21.00%	21.00%
Effective income tax rate reconciliation, percent	34.70%	0.09%	24.70%	4.06%
Income tax (expense) benefit	$ (2,701)	$ 7	$ (3,785)	$ (2,596)
Income before income taxes	7,783	7,903	15,344	64,012
Unrecognized Tax Benefits	$ 1,752	$ 1,309	$ 1,752	$ 1,309

Share-Based Compensation (Detai

Share-Based Compensation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	Apr. 01, 2021	Oct. 01, 2020	Dec. 21, 2018	Oct. 01, 2018	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2020	Feb. 18, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value, exercises in period							$ 43,564
Employee Stock Ownership Plan (ESOP), Shares in ESOP			11,297
Common stock, par value (in dollars per share)					$ 0.01		$ 0.01		$ 0.01
Non-cash share-based compensation					$ 3,214	$ 2,304	$ 6,233	$ 5,984
Share-based Compensation expense					3,214	2,326	6,290	6,017
Compensation cost not yet recognized, period for recognition					$ 19,110		19,110
Fair value of options vested							4,326
Proceeds from issuance of common stock							$ 13,430	8,333
Employee Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Stock Ownership Plan (ESOP), Shares in ESOP			5,000
Equity incentive plan, number of shares authorized (shares)					5,100		5,100			5,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant					4,990		4,990
Purchase price of stock, percentage				85.00%
Purchase period				6 months
Employee Stock Ownership Plan (ESOP), Compensation Expense					$ 187	$ 35	$ 403	$ 74
Shares issued under ESPP	62	120
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity incentive plan, number of shares authorized (shares)					11,083		11,083
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant					2,177		2,177
Compensation cost not yet recognized, period for recognition					$ 11,897		$ 11,897
Period for recognition for unrecognized compensation expense							2 years 6 months
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period for recognition for unrecognized compensation expense							2 years 7 months 6 days
Vested in period (shares)							234
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, par value (in dollars per share)			$ 0.01
Evoqua Water Technologies Corp. Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual term of options							10 years
Stock awards vesting percentage					25.00%

Share-Based Compensation (Stock

Share-Based Compensation (Stock Option Activity) (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2020
Share-based Payment Arrangement [Abstract]
Intrinsic value, exercises in period	$ 43,564
Options
Outstanding at beginning of the period (shares)	7,430,000
Granted (shares)	611,000
Exercised (shares)	(2,185,000)
Forfeited (shares)	(7,000)
Outstanding at end of the period (shares)	5,849,000
Options exercisable (shares)	3,857,000
Options vested and expected to vest (shares)	5,774,000
Weighted Average Exercise Price/Share
Weighted average exercise price, outstanding, beginning balance (in dollars per share)	$ 10.30
Weighted average exercise price, granted (in dollars per share)	24.76
Weighted average exercise price, exercised (in dollars per share)	6.04
Weighted average exercise price, forfeited (in dollars per share)	19.20
Weighted average exercise price, outstanding, ending balance (in dollars per share)	13.39
Weighted average exercise price, exercisable (in dollars per share)	9.62
Weighted average exercise price, options vested and expected to vest (in dollars per share)	$ 13.25
Weighted Average Remaining Contractual Term
Weighted average remaining contractual term, outstanding	6 years 4 months 24 days	5 years 10 months 24 days
Weighted average contractual term, exercisable	5 years 2 months 12 days
Weighted average remaining contractual term, options vested and expected to vest	6 years 3 months 18 days
Intrinsic value, outstanding	$ 75,542		$ 83,152
Intrinsic value, exercisable	64,333
Intrinsic value, options vested and expected to vest	$ 75,349

Share-Based Compensation (Nonve

Share-Based Compensation (Nonvested Share Activity) (Details)	6 Months Ended
	Mar. 31, 2021$ / sharesshares
Shares
Nonvested at beginning of period | shares	2,166,000
Granted (shares) | shares	611,000
Vested (shares) | shares	(778,000)
Forfeited (shares) | shares	(7,000)
Nonvested at end of period | shares	1,992,000
Weighted Average Grant Date Fair Value/Share
Weighted average grant date fair value, nonvested, beginning balance (in dollars per share) | $ / shares	$ 5.56
Weighted average grant date fair value, granted (in dollars per share) | $ / shares	8.98
Weighted average grant date fair value, vested (in dollars per share) | $ / shares	5.56
Weighted average grant date fair value, forfeited (in dollars per share) | $ / shares	6.47
Weighted average grant date fair value, nonvested, ending balance (in dollars per share) | $ / shares	$ 6.60

Share-Based Compensation (RSU A

Share-Based Compensation (RSU Activity) (Details) shares in Thousands	6 Months Ended
	Mar. 31, 2021$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options exercisable (shares) | shares	3,857
Shares
Forfeited | shares	7
Weighted Average Grant Date Fair Value/Share
Weighted average grant date fair value, forfeited (in dollars per share) | $ / shares	$ 6.47
Weighted average exercise price, options vested and expected to vest (in dollars per share) | $ / shares	$ 13.25
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options exercisable (shares) | shares	948
Shares
Outstanding at beginning of the period (shares) | shares	750
Granted | shares	494
Vested in period (shares) | shares	(234)
Forfeited | shares	3
Outstanding at beginning of the period | shares	1,000
Weighted Average Grant Date Fair Value/Share
Weighted average grant date fair value, nonvested, equity instruments other than options, beginning of the period (in dollar per share) | $ / shares	$ 17.86
Weighted average grant date fair value, granted (in dollars per share) | $ / shares	24.69
Weighted average grant date fair value, vested (in dollars per share) | $ / shares	17.64
Weighted average grant date fair value, forfeited (in dollars per share) | $ / shares	18.85
Weighted average grant date fair value, nonvested, equity instruments other than options, end of the period (in dollar per share) | $ / shares	21.26
Weighted average exercise price, options vested and expected to vest (in dollars per share) | $ / shares	$ 21.11
Cancelled (shares) | shares	(7)
Weighted average exercise price, cancelled (in dollars per share) | $ / shares	$ 21.22

Concentration of Credit Risk (D

Concentration of Credit Risk (Details)	Mar. 31, 2021country
Risks and Uncertainties [Abstract]
Number of countries in which entity operates	10

Commitments and Contingencies_2

Commitments and Contingencies (Schedule of Letters of Credit and Surety Bonds) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Sep. 30, 2020
Other Commitments [Line Items]
Debt instrument, unused borrowing capacity, amount	$ 33,096	$ 32,037
Line of credit facility, remaining borrowing capacity	45,000	45,000
Surety Bond [Member]
Other Commitments [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	250,000	230,000
Guarantor Obligations, Current Carrying Value	147,565	152,990
Guarantor Obligations, Remaining Surety Bonds Available	$ 102,435	77,010
Minimum | Surety Bond [Member]
Other Commitments [Line Items]
Letter of Credit, Guarantee, Bond Commitments, Expiration Period	12 months
Maximum | Surety Bond [Member]
Other Commitments [Line Items]
Letter of Credit, Guarantee, Bond Commitments, Expiration Period	10 years
Letter of Credit
Other Commitments [Line Items]
Letters of credit outstanding, amount	$ 11,904	12,963
Debt instrument, unused borrowing capacity, amount	$ 113,096	$ 112,037

Accrued Expenses and Other Li_3

Accrued Expenses and Other Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Sep. 30, 2020
Payables and Accruals [Abstract]
Salaries, wages and other benefits	$ 59,245	$ 67,766
Obligation under operating leases	13,119	12,767
Obligation under finance leases	11,869	11,362
Third party commissions	9,192	9,270
Insurance liabilities	3,760	3,954
Fair value of liability derivatives	166	4,716
Taxes, other than income	3,939	5,316
Provisions for litigation	2,072	2,580
Severance payments	1,185	970
Earn-outs related to acquisitions	295	295
Other	28,360	24,393
Accrued expenses and other liabilities	$ 134,692	$ 143,389
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Accrued expenses and other liabilities	Accrued expenses and other liabilities
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	Accrued expenses and other liabilities
Option and Purchase Right	$ 1,490	$ 0

Business Segments (Details)

Business Segments (Details) $ in Thousands	Oct. 29, 2018segment	Mar. 31, 2021USD ($)segment	Mar. 31, 2020USD ($)	Mar. 31, 2021USD ($)segment	Mar. 31, 2020USD ($)	Sep. 30, 2020USD ($)
Segment Reporting [Abstract]
Number of reportable segments | segment	3	2		2
Segment Reporting Information [Line Items]
Revenue from product sales and services		$ 346,564	$ 351,663	$ 668,757	$ 697,768
Operating profit (loss)		16,178	21,155	32,412	90,847
Interest expense		(8,395)	(13,252)	(17,068)	(26,835)
Income (loss) before income taxes		7,783	7,903	15,344	64,012
Income tax (expense) benefit		(2,701)	7	(3,785)	(2,596)
Net income		5,082	7,910	11,559	61,416
Depreciation and amortization				54,607	52,514
Capital expenditures				36,297	38,759
Assets		1,879,799		1,879,799		$ 1,844,458
Goodwill		404,393		404,393		397,205
Integrated Solutions and Services
Segment Reporting Information [Line Items]
Revenue from product sales and services		224,134	237,885	438,851	466,023
Applied Product Technologies
Segment Reporting Information [Line Items]
Revenue from product sales and services		122,430	113,778	229,906	231,745
Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenue from product sales and services		27,746	18,585	45,887	42,809
Intersegment Eliminations | Integrated Solutions and Services
Segment Reporting Information [Line Items]
Revenue from product sales and services		4,069	2,939	6,105	6,601
Intersegment Eliminations | Applied Product Technologies
Segment Reporting Information [Line Items]
Revenue from product sales and services		23,677	15,646	39,782	36,208
Operating Segments
Segment Reporting Information [Line Items]
Total revenue		374,310	370,248	714,644	740,577
Operating Segments | Integrated Solutions and Services
Segment Reporting Information [Line Items]
Total revenue		228,203	240,824	444,956	472,624
Revenue from product sales and services		224,134	237,885	438,851
Operating profit (loss)		30,784	36,695	57,141	69,849
Assets		831,558		831,558		835,307
Goodwill		229,449		229,449		224,381
Operating Segments | Applied Product Technologies
Segment Reporting Information [Line Items]
Total revenue		146,107	129,424	269,688	267,953
Revenue from product sales and services		122,430	113,778	229,906
Operating profit (loss)		18,103	23,750	31,483	86,892
Assets		612,320		612,320		598,701
Goodwill		174,944		174,944		172,824
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Operating profit (loss)		(32,709)	$ (39,290)	(56,212)	$ (65,894)
Assets		$ 435,921		$ 435,921		$ 410,450

Earnings per Share (Details)

Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Numerator:
Numerator for basic and diluted earnings per common share—Net income attributable to Evoqua Water Technologies Corp.	$ 5,036	$ 7,812	$ 11,469	$ 60,957
Denominator:
Denominator for basic net income per common share—weighted average shares	118,882	116,459	118,882	116,459
Effect of dilutive securities:
Share‑based compensation	3,041	4,391	3,393	4,892
Denominator for diluted net income per common share—adjusted weighted average shares	121,923	120,850	122,275	121,351
Basic income per common share	$ 0.04	$ 0.07	$ 0.10	$ 0.52
Diluted income per common share	$ 0.04	$ 0.06	$ 0.09	$ 0.50

Subsequent Events (Details)

Subsequent Events (Details) - USD ($)	Apr. 01, 2021	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2020
Subsequent Event [Line Items]
Borrowings under credit facility		$ 0	$ 2,597,000
Total debt		889,427,000		$ 885,470,000
Write off of Deferred Debt Issuance Cost		0	$ 1,795,000
First Lien Term Facility, due December 20, 2024
Subsequent Event [Line Items]
Total debt		$ 814,538,000		$ 819,276,000
Subsequent Event
Subsequent Event [Line Items]
Unamortized Debt Issuance Expense	$ 822,000
Accounts Receivable from Securitization	142,200,000
Subsequent Event | water consulting specialists, inc
Subsequent Event [Line Items]
Cash paid at closing	12,025,000
Subsequent Event | Maximum
Subsequent Event [Line Items]
Accounts Receivable from Securitization	150,000,000
Subsequent Event | Term Loan
Subsequent Event [Line Items]
Borrowings under term loan	475,000,000
Debt instrument, periodic payment, principal	1,188,000
Unamortized Debt Issuance Expense	1,931,000
Payments of Financing Costs	4,985,000
Subsequent Event | Term Loan | 2021 Credit Agreement
Subsequent Event [Line Items]
Amount of loan	475,000,000
Subsequent Event | Term Loan | Interest Expense [Member]
Subsequent Event [Line Items]
Debt Issuance Costs, Gross	3,054,000
Subsequent Event | First Lien Term Facility, due December 20, 2024
Subsequent Event [Line Items]
Write off of Deferred Debt Issuance Cost	1,333,000
Revolving Credit Facility | Subsequent Event
Subsequent Event [Line Items]
Borrowings under credit facility	105,000,000
Revolving Credit Facility | Subsequent Event | 2021 Credit Agreement
Subsequent Event [Line Items]
Credit facility borrowing capacity	350,000,000
Letter of Credit | Subsequent Event | 2021 Credit Agreement
Subsequent Event [Line Items]
Credit facility borrowing capacity	$ 60,000,000