EXHIBIT 5.1
 
                     MCCUTCHEN, DOYLE, BROWN & ENERSEN, LLP
 
February 13, 1998                                         Direct: (650) 849-4820
                                                                wnewell@mdbe.com
 
California Water Service Group
1720 North First Street
San Jose, California 95112
 
                       REGISTRATION STATEMENT ON FORM S-3
 
LADIES AND GENTLEMEN:
 
     We have acted as counsel for California Water Service Group, a California
corporation (the "Company"), in connection with the Registration Statement on
Form S-3 as amended (the "Registration Statement") filed by the Company under
the Securities Act of 1933, relating to the registration of shares of Common
Stock, no par value, of the Company.
 
     We are of the opinion that the foregoing securities have been duly
authorized and, when sold pursuant to the terms described in the Registration
Statement, will be duly and validly issued, fully paid and nonassessable.
 
     We hereby consent to the filing of this opinion as Exhibit 5.1 to the
Registration Statement and to the use of our name under the caption "Legal
Matters" in the Registration Statement and in the Prospectus included therein.
 
                                  Very truly yours,
 
                                  McCUTCHEN, DOYLE, BROWN & ENERSEN, LLP
 
                                  By          /s/ WILLIAM J. NEWELL
                                    --------------------------------------------
                                                A Member of the Firm