Cal. Water Code § 35562

In addition, and as an alternative, to the purposes for which the proceeds from water charges may be used, as set forth in Article 4 (commencing with Section 35470) of Chapter 2 of Part 5 of this division, water charges may be levied and collected in order to provide, in whole or in part, for the payment of amounts due to the United States, whether for capital charges or service charges or otherwise, pursuant to contracts made in accordance with Chapter 6 (commencing with Section 35875) of Part 5 of this division, or in order to provide, in whole or in part, for the payment of the costs of a project or the principal of and interest on bonds or warrants of the district, or to obtain funds for any lawful purpose of the district. The district may, by resolution, make such water charges payable in advance. The district may, by resolution, provide that water charges which remain unpaid for a period of not less than 30 days after they have become due shall be delinquent, and a penalty not in excess of 10 percent shall be added thereto, and they shall bear interest at a rate not in excess of 12 percent per year.