OPINION OF NOSSAMAN, GUTHNER, KNOX & ELLIOTT, LLP

EXHIBIT 5.1

December 17, 1999

Board of Directors of California Water Service Group
c/o Robert W. Foy
Chairman of the Board
California Water Service Group
1720 North First Street
San Jose, CA 95112-4598

Re: California Water Service Group - Post-Effective Amendment No. 1
to Registration Statement on Form S-4 Filed on December 17, 1999
Under The Securities Act of 1933, as Amended.

Gentlemen:

This opinion is being furnished to you in connection with California
Water Service Group's (the "Corporation") Post-Effective Amendment No. 1 to
registration statement on Form S-4 filed on December 17, 1999 (the "Amended
Registration Statement") relating to the issuance of common shares, no par value
(the "Shares"), of the Corporation pursuant to the Agreement and Plan of
Reorganization dated as of November 13, 1998, as amended on March 22, 1999, by
and among the Corporation, California Water Service Company and Dominguez
Services Corporation (the "Amended Reorganization Agreement").

You have requested our opinion as to the legality of the shares being
registered, and as to whether the shares will, when sold, be legally issued,
fully paid and non-assessable.

In rendering this opinion, we have (with your permission) relied upon
and assumed as correct and complete the factual representations and information
contained in (i) the Certificate of Incorporation and Bylaws of the Corporation,
and (ii) the Amended Reorganization Agreement.

We have also made such inquiries and examined originals (or copies
certified or otherwise identified to our satisfaction) of documents, corporate
records and other instruments and made such examination of the law as we have
deemed necessary or appropriate to enable us to render this opinion.

We have assumed that the signatures on the documents we have examined
are genuine and further assumed that at the time of issuance of the Shares the
Corporation will have received the full amount of the consideration therefor in
accordance with the terms of the Amended Reorganization Agreement.

Based upon and subject to the foregoing, we are of the opinion that the
Shares have been duly and validly created and authorized and, when issued, will
be validly issued and outstanding as fully paid and non-assessable common shares
of the Corporation.

This opinion is rendered only to the Corporation in connection with the
filing of the Amended Registration Statement and may not be relied upon by any
other person, firm or entity for any other


purpose without our express written consent, and may not be used, circulated,
quoted or otherwise referred to for any other purpose without our express
written consent.

We hereby consent to the filing of this letter as Exhibit 5.1 to the
Amended Registration Statement and to being named in the Proxy
Statement/Prospectus of the Amended Registration Statement under the heading
"Legal Opinion" as counsel for the corporation.

Very truly yours,

/s/ NOSSAMAN, GUTHNER, KNOX &
ELLIOTT, LLP