California Code, Health and Safety Code - HSC § 5040

The governing body shall establish just and equitable rates for the use and maintenance of the works, to be paid by the person leasing or occupying the building or premises served thereby or that in any way uses or is served by the works, and may change and readjust the rates from time to time. The rates shall be sufficient in each year for the payment of the proper and reasonable expenses of operation, repair, replacement, and maintenance of the works, and for payment of the principal of and the interest on the bonds.