EWG's Tap Water Database — 2021 UPDATE



Marais Des Cygnes Public Utility Authority

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
20140.664 ppm550.540 ppm - 0.800 ppm
20150.634 ppm550.500 ppm - 0.710 ppm
20160.580 ppm550.490 ppm - 0.690 ppm
20170.602 ppm550.440 ppm - 0.720 ppm
20180.610 ppm550.540 ppm - 0.680 ppm
20190.502 ppm550.370 ppm - 0.640 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
2014-01-07325580.760 ppm
2014-04-14960170.610 ppm
2014-05-121127490.610 ppm
2014-07-141501630.800 ppm
2014-10-222176220.540 ppm
2015-01-072588000.650 ppm
2015-04-073092370.710 ppm
2015-05-123318100.500 ppm
2015-07-083630650.690 ppm
2015-10-134217490.620 ppm
2016-01-134758850.520 ppm
2016-04-135273900.590 ppm
2016-05-035376370.490 ppm
2016-07-115804890.610 ppm
2016-10-046350880.690 ppm
2017-01-106800260.630 ppm
2017-04-047340230.720 ppm
2017-05-107595950.560 ppm
2017-07-127964090.440 ppm
2017-10-038520140.660 ppm
2018-01-089042580.680 ppm
2018-04-029382980.580 ppm
2018-05-079666460.540 ppm
2018-07-0910028460.670 ppm
2018-10-0810577400.580 ppm
2019-01-0811028250.390 ppm
2019-04-0811393570.370 ppm
2019-05-0711577870.530 ppm
2019-07-1012017530.640 ppm
2019-10-0812567800.580 ppm