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, 2005, 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 2005 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:  March 9, 2006                   By: /s/ Peter C. Nelson
                                           -----------------------
                                           PETER C. NELSON
                                           President and Chief Executive Officer
                                           California Water Service Group