EXHIBIT 5.1


                        [GOODWIN PROCTER LLP LETTERHEAD]



                                  May 28, 2004



Watts Water Technologies, Inc.
815 Chestnut Street
North Andover, Massachusetts  01845

      Re:   Legality of Securities to be Registered Under Registration Statement
            on Form S-8

Ladies and Gentlemen:

      This opinion is furnished in connection with the registration statement on
Form S-8 (the "Registration Statement") pursuant to the Securities Act of 1933,
as amended (the "Securities Act"), relating to the registration of the sale of
up to an aggregate of 3,000,000 shares (the "Shares") of class A common stock,
par value $0.10 per share, of Watts Water Technologies, Inc., a Delaware
corporation (the "Company"), which may be issued under the Watts Water
Technologies, Inc. 2004 Stock Incentive Plan (the "Plan").

      In connection with rendering this opinion, we have examined (i) the
Restated Certificate of Incorporation of the Company, as amended, as on file
with the Secretary of State of the State of Delaware, (ii) the Amended and
Restated By-laws of the Company, as amended, (iii) such records of the corporate
proceedings of the Company as we deemed material, (iv) the Registration
Statement and the exhibits thereto and the related prospectus, (v) the Plan, and
(vi) such other certificates, receipts, records and documents as we considered
necessary for the purposes of this opinion. In our examination, we have assumed
the genuineness of all signatures, the legal capacity of natural persons, the
authenticity of all documents submitted to us as certified, photostatic or
facsimile copies, the authenticity of the originals of such copies and the
authenticity of telephonic confirmations of public officials and others. As to
facts material to our opinion, we have relied upon certificates or telephonic
confirmations of public officials and certificates, documents, statements and
other information of the Company or representatives or officers thereof.

      We are attorneys admitted to practice in The Commonwealth of
Massachusetts. We express no opinion concerning the laws of any jurisdictions
other than the laws of the United States of America and the Commonwealth of
Massachusetts and the Delaware General Corporation Law (which includes
applicable provisions of the Delaware General Corporation Law and reported
judicial decisions interpreting the Delaware General Corporation Law and
applicable provisions of the Delaware Constitution), and express no opinion with
respect to the blue sky or securities laws of any state, including, without
limitation, Massachusetts and Delaware.



Watts Water Technologies, Inc.
May 28, 2004
Page 2


      Based upon the foregoing, we are of the opinion that upon the issuance and
delivery of the Shares against payment therefor in accordance with the terms of
the Plan, the Shares will be validly issued, fully paid and nonassessable under
the Delaware General Corporation Law.

      The foregoing assumes that all requisite steps will be taken to comply
with the requirements of the Securities Act and applicable requirements of state
laws regulating the offer and sale of securities.

      The opinions expressed herein are being furnished to you solely for your
benefit in connection with the Registration Statement, and may not be used or
relied upon by you for any other purpose. We hereby consent to the inclusion of
this opinion as an exhibit to the Registration Statement. In giving such
consent, we do not thereby admit that we are in the category of persons whose
consent is required under Section 7 of the Securities Act.


                                          Sincerely,

                                          /S/ GOODWIN PROCTER LLP

                                          GOODWIN PROCTER LLP