EWG's Tap Water Database — 2019 UPDATE



City of Lewiston

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
20120.665 ppm440.300 ppm - 0.930 ppm
20130.442 ppm660.00177 ppm - 0.828 ppm
20140.553 ppm660.340 ppm - 0.897 ppm
20150.493 ppm660.288 ppm - 0.929 ppm
20160.552 ppm440.342 ppm - 0.789 ppm
20170.715 ppm550.321 ppm - 0.923 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
2012-04-03I592550.300 ppm
2012-08-15I621760.930 ppm
2012-08-15I621770.500 ppm
2012-08-15I621780.930 ppm
2013-02-27I130228026-0010.479 ppm
2013-06-05I130606050-0010.00177 ppm
2013-06-05I130606050-0020.490 ppm
2013-08-21I130822058-0010.305 ppm
2013-08-21I130822058-0050.551 ppm
2013-08-21I130822058-0040.828 ppm
2014-02-25I140226039-0010.512 ppm
2014-02-25I140226039-0020.897 ppm
2014-06-03I140604041-0020.475 ppm
2014-06-03I140604041-0010.458 ppm
2014-08-13I140814054-0050.633 ppm
2014-08-13I140814054-0040.340 ppm
2015-01-21I150122025-0010.348 ppm
2015-04-21I150422037-0010.929 ppm
2015-06-10I150611032-0020.398 ppm
2015-06-10I150611032-0010.460 ppm
2015-07-22I150723044-0010.288 ppm
2015-07-22I150723044-0030.532 ppm
2016-02-09I160209050-0020.406 ppm
2016-02-09I160209050-0010.789 ppm
2016-04-06I160407008-0010.342 ppm
2016-04-06I160407008-0030.670 ppm
2017-03-28I170328050-0010.923 ppm
2017-03-28I170328050-0020.897 ppm
2017-10-25I171026026-0030.321 ppm
2017-10-25I171026026-0020.867 ppm
2017-10-25I171026026-0010.568 ppm