Cal. Water Code § 37960

The district may, by ordinance, levy groundwater extraction charges, including volumetric charges intended to provide an incentive for reduced water use, on the extraction of groundwater from all water extraction facilities within the territory of the district for the purposes of paying the costs of initiating, carrying on, and completing any of the powers, purposes, and groundwater management activities described in this act. Any groundwater extraction charges shall be uniform for groundwater extraction within the territory of the district.