Cal. Pub. Util. Code § 797
The commission shall periodically audit, or direct that an independent audit be periodically conducted for, all significant transactions, as specified by the commission, between a water corporation with more than 2,000 service connections, or an electrical, gas, or telephone corporation, and every subsidiary or affiliate of, or corporation holding a controlling interest in, that water, electrical, gas, or telephone corporation. The commission, in this connection, may utilize the services of an independent auditor, who shall be selected and supervised by the commission, or may direct a water corporation with more than 2,000 service connections, or an electrical, gas, or telephone corporation, to utilize the services of an independent auditor, who shall be selected and supervised by that water, electrical, gas, or telephone corporation. Nothing in this section prohibits the commission from auditing any transaction between a water corporation with more than 2,000 service connections, or an electrical, gas, or telephone corporation, and any subsidiary or affiliate of, or corporation holding a controlling interest in, that water, electrical, gas, or telephone corporation, as otherwise permitted or required by law.
Ca. Pub. Util. Code § 797