EXHIBIT 32.1

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

     In connection with the Quarterly Report on Form 10-Q for the fiscal quarter ended September 30, 2006 of California Water Service Group (the “Company”) as filed with the Securities and Exchange Commission on the date hereof (the “Report”), I, Peter C. Nelson, Chief Executive Officer of the Company, certify, pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that:

1.

The Report fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

2.

The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

Date: November 9, 2006		/s/ Peter C. Nelson   PETER C. NELSON
		Chief Executive Officer
		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 the Company and furnished to the Securities and Exchange Commission or its staff upon request.