EWG's Tap Water Database — 2021 UPDATE



Knott County Water & Sewer District

Fluoride occurs naturally in surface and groundwater and is also added to drinking water by many water systems. Read More.

Fluoride has been promoted as a chemical that reduces dental cavities. Yet it is now well-established that fluoride primarily exerts its protective effects through topical mechanisms, such as sodium fluoride in toothpaste and mouthwash. In contrast, long-term ingestion of fluoride in water increases dental fluorosis, which includes mottling, pitting and weakening of the teeth. EPA's maximum legal limit is set at 4 parts per million (ppm) to prevent skeletal fluorosis, a condition where bones become brittle and more susceptible to fractures, although these effects may occur at lower doses.

Even fluoride levels of 0.7 ppm, the amount of fluoride in drinking water recommended by the U.S. Public Health Service, can result in too much fluoride for bottle-fed babies. EWG recommends that caregivers mix baby formula with fluoride-free water. The National Toxicology Program is investigating the potential for low doses of fluoride to alter thyroid function and childhood brain development.





Samples exceeding legal limit (MCL)


Samples exceeding
health guidelines

Testing results - average by year

YearAverage resultSamples takenDetectionsRange of results
20140.830 ppm220.820 ppm - 0.840 ppm
20150.805 ppm220.800 ppm - 0.810 ppm
20160.575 ppm220.540 ppm - 0.610 ppm
20170.475 ppm220.350 ppm - 0.600 ppm
20180.760 ppm220.690 ppm - 0.830 ppm
20190.710 ppm220.630 ppm - 0.790 ppm

ppm = parts per million

State and national drinking water standards and health guidelines

EPA Maximum Contaminant
Level (MCL) 4 ppm

ppm = parts per million

All test results

Date Lab ID Result
2014-03-052014031080010.840 ppm
2014-04-022014047170010.820 ppm
2015-03-182015032600010.810 ppm
2015-04-082015042390010.800 ppm
2016-03-022016030290010.540 ppm
2016-04-062016047880010.610 ppm
2017-03-082017032660010.600 ppm
2017-04-052017049120010.350 ppm
2018-03-072018025420010.690 ppm
2018-04-042018037970010.830 ppm
2019-03-05190063280.790 ppm
2019-05-07190129370.630 ppm