CERTIFICATIONS

Exhibit 31.1
CERTIFICATIONS

I, Peter Nelson, President and Chief Executive Officer of California Water
Service Group, certify that:

1. I have reviewed this Annual Report on Form 10-K for the year ended
December 31, 2004 of California Water Service Group;

2. Based on my knowledge, this report does not contain any untrue
statement of a material fact or omit to state a material fact
necessary to make the statements made, in light of the circumstances
under which such statements were made, not misleading with respect to
the period covered by this report;

3. Based on my knowledge, the financial statements, and other financial
information included in this report, fairly present in all material
respects the financial condition, results of operations and cash flows
of the registrant as of, and for, the periods presented in this
report;

4. The registrant's other certifying officer and I are responsible for
establishing and maintaining disclosure controls and procedures (as
defined in Exchange Act Rules 13a-15(e) and 15(d)-15(e)) and internal
control over financial reporting (as defined in Exchange Act Rules
13a-15(f) and 15(d)-15(f)) for the registrant and have:

a. Designed such disclosure controls and procedures, or caused such
disclosure controls and procedures to be designed under our
supervision, to ensure that material information relating to the
registrant, including its consolidated subsidiaries, is made known
to us by others within those entities, particularly during the
period in which this report is being prepared;

b. Designed such internal control over financial reporting, or caused
such internal control over financial reporting to be designed
under our supervision, to provide reasonable assurance regarding
the reliability of financial reporting and the preparation of
financial statements for external purposes in accordance with
generally accepted accounting principles;

c. Evaluated the effectiveness of the registrant's disclosure
controls and procedures and presented in this report our
conclusions about the effectiveness of the disclosure controls and
procedures, as of the end of the period covered in this report
based on such evaluation; and

d. Disclosed in this report any change in the registrant's internal
control over financial reporting that occurred during the fourth
fiscal quarter of 2004 that has materially affected, or is
reasonably likely to materially affect, the registrant's internal
control over financial reporting; and

5. The registrant's other certifying officer and I have disclosed, based
on our most recent evaluation of internal control over financial
reporting, to the registrant's auditors and the audit committee of the
registrant's board of directors (or persons performing the equivalent
functions):

a. All significant deficiencies and material weaknesses in the design
or operation of internal control over financial reporting which
are reasonably likely to adversely affect the registrant's ability
to record, process, summarize and report financial information;
and


b. Any fraud, whether or not material, that involves management or
other employees who have a significant role in the registrant's
internal control over financial reporting.


Date: February 23, 2005 By: /s/ Peter C. Nelson
PETER C. NELSON
President and Chief Executive Officer
California Water Service Group