Cal. PUC § 12814

A district may add fluorine or fluorine compounds to the water supply of the district only if the voters of the district have approved the addition of the fluorine and fluorine compounds to the water supply. If a majority of the voters of a district voting upon the proposition at an election called and held as prescribed in Section 12815 have voted in favor of the addition of fluorine and fluorine compounds to the water supply of the district, the district shall, subject to Article 1 (commencing with Section 116275), of Chapter 4 of Part 12 of Division 104 of, and Sections 116325, 116340, 116345, and 116500 of, the Health and Safety Code, add to water intended for consumption or use by the public, including domestic, industrial, and other uses, fluorine and fluorine compounds.