California Code, Health and Safety Code - HSC § 5029

(a) The payment or providing for payment, including payments into any reserve or sinking funds, as the same falls due, of the principal of and the interest on the bonds;

(b) The management, maintenance, operation and repair costs of the works.

After provision has been made for the payment of the foregoing, any surplus remaining may be used as follows: (a) for the purchase in the open market of the outstanding unmatured bonds of the district; (b) for extensions, or for the enlargement, replacement or betterment of the works; (c) for any lawful purpose of the district.