California Code, Public Utilities Code - PUC § 314.5

(a)(1) The commission shall apply a risk-based methodology to conduct audits or reviews of the books and records of electrical, gas, telephone, water, and sewer corporations.

(2) The commission shall conduct a review or audit of the books and records of every electrical or gas corporation at least once every five years.

(3) The commission shall conduct an audit or review of the books and records of every high-risk telephone, water, or sewer corporation, as determined by the commission, during the regular regulatory review of those entities, at least once every 10 years.