California Code, Public Utilities Code - PUC § 2706

(a) Any person, firm, or corporation, their lessees, trustees, receivers or trustees appointed by any court, who sells or delivers water exclusively to a water conservation district organized under the laws of the state or who leases or otherwise permits the use of ditches or other water transmission facilities exclusively by the district is not a public utility within the meaning of this chapter. No portion of the works, property, or water rights of any of those parties shall be deemed dedicated to a public use by reason of selling or delivering water to a water conservation district.

(b) Any person, firm, or corporation with water that is not being used to supply water to a public water system, or that is not otherwise dedicated to public use, that sells, leases, transfers, or otherwise delivers the water at wholesale to any public agency or to a water corporation providing water utility service, is not a public utility within the meaning of this chapter.

(c) This section does not apply to mutual water companies.