Tenn. Code § 28-3-302
Notwithstanding any other provision of law to the contrary, if gallonage for water or sewer service or both is inaccurately recorded or registered due to equipment failure and results in the customer being undercharged or overcharged, and the customer is unaware of the error, defect or failure, no utility district, municipality, or water or sewer system or company shall be authorized to collect or assess a charge for the unpaid gallonage or to reimburse the customer for overpayment of such usage, prior to thirty-six (36) months from the date the error is discovered and billed; provided, that if a date certain can be established for such error which is less than thirty-six (36) months, no utility district, municipality, or water or sewer system or company shall be authorized to collect or assess a charge for such usage, or to reimburse the customer for overpayment of such usage, beyond such date.
T.C.A. § 28-3-302