Cal. Wat. Code § 31031
A district may, pursuant to the notice, protest, and hearing procedures in Section 53753 of the Government Code, fix, on or before the first day of July in each calendar year, a water standby or availability charge. The water standby or availability charge shall not exceed ten dollars ($10) per acre per year for each acre of land, or ten dollars ($10) per year for each parcel of land less than an acre within the district to which water is made available for any purpose by the district, whether the water is actually used or not, unless the standby charge is imposed pursuant to the Uniform Standby Charge Procedures Act (Chapter 12.4 (commencing with Section 54984) of Part 1 of Division 2 of Title 5 of the Government Code). The board of directors of a district which fixes such a charge may establish schedules varying such charge according to the land uses and the degree of availability or quantity of use of such water to the affected lands, and may restrict such charge to lands lying within one or more improvement districts within such district. If the procedures set forth in this section as it read at the time a standby or immediate availability charge was established were followed, the board of directors may, by resolution, continue the charge in successive years at the same rate. If new, increased, or extended assessments are proposed, the board shall comply with the notice, protest, and hearing procedures in Section 53753 of the Government Code.
Ca. Water Code § 31031