Cal. Pub. Util. Code § 1506

As used in this chapter, “private utility” includes a mutual water company. In its application to mutual water companies, this chapter affects and relates only to the property, or portion of any property, of a mutual water company that is employed by the company in providing water service in or for a territory that is actually being provided with water service by the company when a political subdivision constructs facilities to provide or extend water service or provides or extends such service to the territory, and that territory shall constitute the “service area” of a mutual water company as used in Section 1502.