Wat. Code, § 50904

A district may, by resolution of the board, provide a procedure for and collect charges and fees, by way of the tax bills of the county or counties in which such district is located. A district may also collect assessments levied under Part 7 (commencing with Section 51200) of the division by way of the tax bills of the county or counties in which such district is located. Such charges and fees or assessments shall appear as a separate item on the tax bill, shall be collected at the same time and in the same manner as county ad valorem property taxes are collected, and shall be subject to the same penalties and the same procedure and sale in case of delinquency as provided for such taxes. The district shall, on or before August 1st of each year, certify to the county auditor the charges and fees or assessments to be collected. The county may deduct from the revenue so collected for the district an appropriate amount for the billing and collection services rendered to the district.