The commission shall inspect and audit the books and records for regulatory and tax purposes (a)at least once in every three years in the case of every electrical, gas, heat, telegraph, telephone, and water corporation serving over 1,000 customers, and (b)at least once in every five years in the case of every electrical, gas, heat, telegraph, telephone, and water corporation serving 1,000 or fewer customers. An audit conducted in connection with a rate proceeding shall be deemed to fulfill the requirements of this
section. Reports of such inspections and audits and other pertinent information shall be furnished to the State Board of Equalization for use in the assessment of public utilities.