Our File No. 2003513-2035130163
June 24, 2004


Via Facsimile

California Water Service Group
1720 North First Street
San Jose, CA  95112

Public Offering of Common Stock by California Water Service Group

Ladies and Gentlemen:


We have  acted as  counsel  for  California  Water  Service  Group,  a  Delaware
corporation  (the  "Company"),  in  connection  with  the  issuance  and sale of
1,250,000  shares of common  stock of the  Company  (the  "Shares")  in a public
offering  pursuant to a shelf  Registration  Statement on Form S-3 (Registration
No.  333-103721) (the  "Registration  Statement")  filed with the Securities and
Exchange  Commission (the "Commission") on March 11, 2003 and declared effective
by the Commission on July 11, 2003;  and pursuant to the  Prospectus  Supplement
dated June 24,  2004 (the  "Prospectus  Supplement")  filed with the  Commission
relating  to  the  issuance  and  sale  of  the  Shares;  and  pursuant  to  the
Underwriting  Agreement  dated August 4, 2003 and the Terms Agreement dated June
24, 2004 (the "Underwriting  Agreement")  between the Company and A.G. Edwards &
Sons,  Inc.  acting on behalf of themselves  and as the  representatives  of the
several underwriters named in such Underwriting Agreement.


As counsel to the Company,  we have reviewed the corporate  proceedings taken by
the Company with respect to the  authorization of the issuance of the Shares. We
have also examined and relied upon such corporate records, documents, agreements
or other instruments of the Company as we have deemed necessary or advisable for
purposes  of  this  opinion.  As to  all  matters  of  fact  (including  factual
conclusions and  characterizations  and  descriptions  of purpose,  intention or
other state of mind) we have entirely  relied upon  certificates  of officers of
the Company,  and have assumed,  without  independent  inquiry,  the accuracy of
those certificates.



California Water Service Group
June 24, 2004
Page 2


In rendering  the opinions  hereinafter  expressed,  we have examined and relied
upon  originals or copies of such  documents and  instruments  as we have deemed
appropriate, including the following documents and instruments:


A. The Certificate of  Incorporation  of the Company,  certified by the Delaware
Secretary of State on June 15, 2004.

B. The  Certificate  of Good  Standing of the  Company,  issued by the  Delaware
Secretary of State on June 15, 2004.

C. The By-Laws of the Company, certified by the Secretary of the Company on June
24, 2004.

D. Records of  proceedings  and actions of the Board of Directors of the Company
on February 26, 2003 and May 26, 2004 and of the Finance  Committee of the Board
of Directors of the Company on June 23, 2004 (the "Resolutions").



We have  assumed  the  genuineness  of all  signatures,  the  conformity  to the
originals  of all  documents  reviewed  by us as copies,  the  authenticity  and
completeness of all original  documents  reviewed by us in original or copy form
and the legal competence of each individual executing a document.

This opinion is limited  solely to the General  Corporation  Law of the State of
Delaware as applied by courts located in Delaware,  the applicable provisions of
the Delaware Constitution and the reported judicial decisions interpreting those
laws.

We  express  no  opinion  as to the  effect of events  occurring,  circumstances
arising,  or changes of law  becoming  effective  or  occurring,  after the date
hereof  on the  matters  addressed  in this  opinion  letter,  and we  assume no
responsibility  to inform you of additional or changed facts, or changes in law,
of which we may become aware.


Subject to the  foregoing,  it is our  opinion  that the  Shares  have been duly
authorized  by the  Company's  Board  of  Directors  and the  Finance  Committee
thereof, and, upon issuance of the Shares in accordance with the Resolutions and
for the consideration  recited therein,  will be validly issued,  fully paid and
nonassessable.





California Water Service Group
June 24, 2004
Page 3


We hereby  consent  to the  filing of this  opinion  as an  exhibit to a Current
Report  on Form 8-K to be filed by you and  incorporated  into the  Registration
Statement,  and to the reference to this firm under the heading "Legal  Matters"
in the Prospectus Supplement. In rendering this opinion and giving this consent,
we do not admit that we are an  "expert"  within the meaning of Section 7 of the
Securities Act and the Rules of the Commission thereunder.


Very truly yours,


/s/ Bingham McCutchen LLP
- -------------------------
BINGHAM McCUTCHEN LLP

cc:    Richard D. Nye
       Vice President, Chief Financial Officer
       and Treasurer
       California Water Service Group