Cal. Water Code § 35520.42

In addition to and as an alternative to all other powers contained in this chapter with respect to provision of funds for the purpose of the care, operation, management, and improvement of a project or projects undertaken under the authority of this chapter, including the payment of salaries of officers and employees and all other expenses, and for the payment of principal of and interest on any bonds issued under this chapter, zones may be established within the drainage service area for the purpose of fixing rates of assessment in accordance with the extent of benefits derived, or to be derived, by each zone from services to the land in each zone arising from the service area’s plan of works or any separately identifiable part thereof.