Cal. Water Code § 75591

If the board determines that a zone or zones should be established and a ground water charge levied therein, it shall establish the zone or zones and levy, assess, and affix the charge against all persons operating ground water-producing facilities within the zone or zones during the current or ensuing water year. However, the board may waive any minimal charge, the collection of which is determined by the board not to result in net economic benefit to the district.