Cal. Water Code § 35520.38

For the purpose of the care, operation, management, and improvement of a project or projects, including 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, the board may, in lieu, either in part or in whole, of calling assessments as provided for in this chapter, fix rates of tolls and charges for drainage facilities or available drainage facilities and other services rendered by the district and collect the tolls and charges from all persons receiving the benefit of the drainage facilities or other services. The tolls and charges shall be proportional as nearly as possible to the services rendered.