Exhibit 5

August 10, 2005


                                                 Our File No. 2003513-2035130005

California Water Service Group
1720 North First Street
San Jose, CA 95112-4598


Registration Statement on Form S-8 for California Water Service Group
Equity Incentive Plan

Ladies and Gentlemen:


We have  acted  as  counsel  to  California  Water  Service  Group,  a  Delaware
corporation (the "Company"), in connection with the Registration Statement under
the Securities Act of 1933, as amended (the "Act"),  of shares (the "Shares") of
the  Company's  Common  Stock,  par value  $0.01 per share,  issuable  under the
Company's  Equity Incentive Plan,  pursuant to a Registration  Statement on Form
S-8 to be filed by the Company with the Securities and Exchange Commission on or
about the date of this opinion.

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  originals or copies,  certified or otherwise
authenticated  to  our  satisfaction,  of  such  corporate  records,  documents,
agreements  or other  instruments  of the Company and of public  officials 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.

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.  We have also
assumed  that  the  registration  requirements  of the Act  and  all  applicable
requirements of state laws regulating the sale of securities will have been duly
satisfied.



California Water Service Group
August 10, 2005
Page 2


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. Subject to the foregoing, it is our opinion that the Shares have been duly
authorized  and, upon issuance of the Shares in accordance with the terms of the
Plans, will be validly issued, fully paid and nonassessable.

We  hereby  consent  to  the  filing  of  this  opinion  as an  exhibit  to  the
Registration  Statement.  In giving our consent, we do not thereby admit that we
are in the category of persons whose consent is required  under Section 7 of the
Act or the rules and  regulations  of the  Securities  and  Exchange  Commission
thereunder.


Very truly yours,



/s/BINGHAM MCCUTCHEN LLP
BINGHAM McCUTCHEN LLP