EXHIBIT 5.1

            OPINION OF McCUTCHEN, DOYLE, BROWN & ENERSEN, LLP AS TO
                           LEGALITY OF THE SECURITIES

                     McCutchen, Doyle, Brown & Enersen, LLP
                                 2100 Geng Road
                          Palo Alto, California 94303


March 6, 1997


California Water Service Group
1720 N. First Street
San Jose, California  95112

Ladies and Gentlemen:

                  California Water Service Group, a California corporation
("Holding Company"), has requested our opinion in connection with a Registration
Statement on Form S-4 (the "Registration Statement") filed by it today with the
Securities and Exchange Commission (the "Commission") under the Securities Act
of 1933, as amended (the "Act"), relating to the shares of its Common Stock, no
par value, and its Preferred Stock, par value $25 (the "Holding Company Common
Stock" and the "Holding Company Preferred Stock," respectively), to be issued in
connection with the merger (the "Merger") of CWSG Merger Company, a California
corporation ("Merger Company") into California Water Service Company, a
California corporation ("Cal Water"), pursuant to the Agreement of Merger dated
as of March 6, 1997, among Cal Water, Holding Company and Merger Company
("Agreement").

                  We have examined and are relying on originals, or copies which
have been certified or otherwise identified to our satisfaction, of the
Agreement, the Restated Articles of Incorporation and Bylaws of the Holding
Company and such other corporate records, such other instruments, certificates
and representations of public officials, officers and representatives of Holding
Company and such other persons, and we have made such investigations of law, as
we have deemed appropriate as a basis for the opinion expressed below.

                  Based on the foregoing, it is our opinion that the shares of
Holding Company Common Stock and Holding Company Preferred Stock to be issued
upon consummation of the Merger pursuant to and in accordance with the Agreement
will upon such consummation be duly authorized, validly issued, fully paid and
non-assessable.

                  We hereby consent to the filing of this opinion as an exhibit
to the Registration Statement. By giving such consent, we do not hereby admit
that we are experts with respect


                  to any part of the Registration Statement within the meaning
of the term "expert" as used in the Act or the rules and regulations of the
Commission issued thereunder.



                                Very truly yours,
                                McCUTCHEN, DOYLE, BROWN & ENERSEN, LLP




                                By: /s/ WILLIAM J. NEWELL
                                   ------------------------------
                                       A Member of the Firm