Cal. Water Code § 72072.3

The board hereby is authorized to impose a tax upon every person using water within any of the improvement districts established by this chapter or on every person using water within the service area of any retail water purveyor within any such improvement district, at the rate and in the manner provided in this article. The tax imposed by this section shall be a percentage of the charges made for such use of water and shall be paid by the person paying for such water.