Tennessee Code Title 68. Health, Safety and Environmental Protection § 68-221-709

(a) If the quarterly analysis of a water sample from a public water system by a certified laboratory confirms that the level of fluoride in the sample exceeds one and one-half milligrams per liter (1.5 mg/L), the public water system from which the sample was taken must:

(b) Once the monthly analysis of water samples for fluoride conducted pursuant to subdivision (a)(1) confirms that the fluoride level in samples is less than one and one-half milligrams per liter (1.5 mg/L) for three (3) consecutive months, the public water system may resume quarterly laboratory analysis for fluoride.