Form: 10-Q

Quarterly report pursuant to Section 13 or 15(d)

May 15, 2003

CERTIFICATION OF CEO AND CFO

Published on May 15, 2003


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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