OPINION OF BINGHAM MCCUTCHEN LLP

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