California Code, Public Utilities Code - PUC § 2713

(a) No water corporation subject to the jurisdiction and control of the commission and the provisions of Part 1 (commencing with Section 201) of this division shall make any charge upon any entity providing fire protection service to others for furnishing water for such fire protection purposes or for any costs of operation, installation, capital, maintenance, repair, alteration, or replacement of facilities related to furnishing water for such fire protection purposes within the service area of such water corporation, except pursuant to a written agreement with such entity providing fire protection services. A water corporation shall furnish water for fire protection purposes to the extent of its means and as a condition of a certificate of public convenience and necessity, in case of fire or other great necessity, within the boundaries of the territory served by it for use within such territory.

(b) The provisions of subdivision (a) shall not restrict or limit a water corporation furnishing water for fire protection purposes from levying charges for water service or facilities, including water for fire protection purposes, on any person, property, or entity, whether public or private, other than on an entity providing fire protection service.

Such charges shall be collected from such other persons, property, or entities pursuant to existing provisions of law which authorize such charges, or from an entity providing fire protection services only pursuant to a written agreement authorizing such charges.

(c) For the purposes of this section, “entity providing fire protection service” means a city, county, city and county, whether general law or chartered, and a fire company, fire protection district, or any other person, association, company, corporation, special district, municipal corporation, or any other public or private entity, which public or private entity or person provides fire protection services to any other public or private entity or person.