Cal. Wat. Code § 56115
In any year, at least 15 days before the first day of the month in which the board of supervisors of the county in which the district is located, is required by law to levy the amount of taxes required by law for county purposes, the district board may furnish to the board of supervisors a written statement of the amount necessary to maintain, operate, extend, or repair any work or improvements of the district, and to defray all other expenses incidental to the exercise of any of the district's powers, and the board of supervisors of the county shall at the time and in the manner of levying other county taxes, levy and cause to be collected a tax upon the taxable real property in the district based upon the last equalized assessment roll of the county sufficient to pay the cost of maintaining, operating, extending, or repairing any work or improvements of the district and of defraying all other expenses incidental to the exercise of any of the district's powers. The tax authorized by this section shall not exceed twenty-five cents ($0.25) for each one hundred dollars ($100) of assessed value on taxable real property in any one year.
Ca. Water Code § 56115