Cal. Wat. Code § 23915
In addition to the charges authorized to be fixed and collected pursuant to Article 3 (commencing with Section 22280) Chapter 2, Part 5 of this division, the board in lieu, in whole or in part, of raising money for the payment of the principal of and interest on bonds of the district issued for an improvement district or for the operating expenses of the improvement district, may fix and collect charges for the making of water available to the holders of title to land in the improvement district or the occupants thereon. Such additional charges within an improvement district shall be fixed and collected in substantially the same manner and upon the same terms and conditions as is provided in Article 3 (commencing with Section 22280), Chapter 2, Part 5 of this division for charges to be fixed and collected within the entire district, except that such additional charges fixed and collected from an improvement district shall be expended only for the payment of the principal of and interest upon bonds of the district issued for the improvement district or for payment of the operating expenses of the improvement district.
Ca. Water Code § 23915