Exhibit 99.1


                            CERTIFICATION PURSUANT TO
                           --------------------------
                             18 U.S.C. SECTION 1350
                             AS ADOPTED PURSUANT TO
                  SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002



                                  CERTIFICATION
                       PURSUANT TO 18 U.S.C. SECTION 1350,
                       AS ADOPTED PURSUANT TO SECTION 906
                        OF THE SARBANES-OXLEY ACT OF 2002


Pursuant  to  Section  906  of  the  Sarbanes-Oxley  Act of  2002,  each  of the
undersigned  certifies  that  this  periodic  report  fully  complies  with  the
requirements  of  Section  13(a) or  15(d),  as  applicable,  of the  Securities
Exchange Act of 1934 and that the information contained in this quarterly report
on Form 10-Q fairly presents, in all material respects,  the financial condition
and results of operations of California Water Service Group.

A signed  original of this  written  statement  required by Section 906 has been
provided to  California  Water  Service Group and will be retained by California
Water Service Group and furnished to the Securities  and Exchange  Commission or
its staff upon request.


Date: May 13, 2003                  /s/ Peter C. Nelson
                                    PETER C. NELSON
                                    Chief Executive Officer
                                    California Water Service Group



Date: May 13, 2003                  /s/  Richard D. Nye
                                    RICHARD D. NYE
                                    Chief Financial Officer
                                    California Water Service Group






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