EWG's Tap Water Database



Missouri American St. Louis County & St. Charles County

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
20101.06 ppm16161.000 ppm - 1.50 ppm
20110.985 ppm20200.900 ppm - 1.10 ppm
20120.723 ppm20200.660 ppm - 0.800 ppm
20130.728 ppm16160.640 ppm - 0.800 ppm
20140.617 ppm27270.560 ppm - 0.700 ppm
20150.606 ppm17170.520 ppm - 0.680 ppm

ppm = parts per million.

State and national drinking water standards and health guidelines

EPA Maximum Contaminant
Level (MCL) 4 ppm

The enforceable federal standard that defines the highest level of a contaminant allowed in drinking water.

ppm = parts per million.

EPA Maximum Contaminant
Level Goal (MCLG)4 ppm

A non-enforceable federal health guideline. For cancer-causing chemicals, these health goals are typically set to zero.

ppm = parts per million.

All test results

Date Lab ID Result
2010-02-02CO037341.40 ppm
2010-04-22CP178811.000 ppm
2010-04-22CP180061.000 ppm
2010-04-22CP180921.000 ppm
2010-04-22CP180951.000 ppm
2010-07-20CP505901.000 ppm
2010-07-20CP506511.000 ppm
2010-07-20CP507561.000 ppm
2010-07-21CP505071.000 ppm
2010-08-09CP678021.000 ppm
2010-08-16CP584741.50 ppm
2010-10-04CP802781.000 ppm
2010-10-05CP802121.000 ppm
2010-10-05CP803391.000 ppm
2010-10-05CP804291.000 ppm
2010-10-05CP804261.000 ppm
2011-01-12CR177241.000 ppm
2011-01-12CR177921.000 ppm
2011-01-12CR178531.10 ppm
2011-01-12CR179401.000 ppm
2011-01-12CR179431.000 ppm
2011-04-05CS270640.900 ppm
2011-04-05CS271250.900 ppm
2011-04-05CS271801.000 ppm
2011-04-05CS272571.000 ppm
2011-04-05CS272600.900 ppm
2011-07-06CS617921.000 ppm
2011-07-06CS618721.000 ppm
2011-07-06CS619280.900 ppm
2011-07-06CS620241.000 ppm
2011-07-06CS620271.000 ppm
2011-10-03CS995101.000 ppm
2011-10-03CS995731.000 ppm
2011-10-03CS996301.000 ppm
2011-10-03CS997091.000 ppm
2011-10-03CS997121.000 ppm
2012-01-05155872010.700 ppm
2012-01-05155953010.700 ppm
2012-01-05158253010.700 ppm
2012-01-05158277010.700 ppm
2012-01-05158288010.700 ppm
2012-04-10164204010.760 ppm
2012-04-10174064010.750 ppm
2012-04-10174082010.760 ppm
2012-04-16161137010.740 ppm
2012-04-16161156010.770 ppm
2012-07-05174065010.710 ppm
2012-07-05174083010.800 ppm
2012-07-05191806010.660 ppm
2012-07-11171317010.720 ppm
2012-07-17169925010.700 ppm
2012-10-09191807010.720 ppm
2012-10-09198927010.680 ppm
2012-10-09198936010.730 ppm
2012-10-09198948010.740 ppm
2012-10-09198954010.720 ppm
2013-02-11212499010.760 ppm
2013-03-13212868010.800 ppm
2013-04-02214901010.770 ppm
2013-04-02214907010.660 ppm
2013-04-02214925010.780 ppm
2013-04-03214916010.720 ppm
2013-04-03214934010.770 ppm
2013-04-22218336010.700 ppm
2013-05-22217971010.790 ppm
2013-06-19224042010.700 ppm
2013-07-10225650010.730 ppm
2013-08-07234641010.760 ppm
2013-09-05234891010.720 ppm
2013-10-08236388010.700 ppm
2013-11-06239312010.640 ppm
2013-12-10241829010.650 ppm
2014-01-15245909010.680 ppm
2014-02-19246908010.560 ppm
2014-03-19249713010.600 ppm
2014-04-15251432010.640 ppm
2014-04-15251441010.630 ppm
2014-04-15251444010.630 ppm
2014-04-16251409010.600 ppm
2014-04-16251414010.580 ppm
2014-04-16251423010.580 ppm
2014-05-14255918010.610 ppm
2014-06-19258565010.620 ppm
2014-07-23261425010.590 ppm
2014-07-23AC293610.670 ppm
2014-07-23AC293620.580 ppm
2014-07-23AC293630.620 ppm
2014-07-23AC293640.660 ppm
2014-07-23AC293650.700 ppm
2014-07-29269563010.630 ppm
2014-07-29269564010.650 ppm
2014-07-29269565010.660 ppm
2014-07-29269566010.650 ppm
2014-07-29269567010.630 ppm
2014-08-19265475010.580 ppm
2014-09-09269058010.590 ppm
2014-10-09271592010.570 ppm
2014-11-06273800010.570 ppm
2014-12-04276544010.580 ppm
2015-01-13282730010.590 ppm
2015-02-12281531010.600 ppm
2015-03-10284121010.570 ppm
2015-04-22286242010.620 ppm
2015-04-22286256010.580 ppm
2015-04-22286247010.610 ppm
2015-04-22286265010.610 ppm
2015-04-22286274010.650 ppm
2015-04-22286277010.520 ppm
2015-05-12288843010.620 ppm
2015-06-04291880010.620 ppm
2015-07-16294613010.550 ppm
2015-08-25298011010.630 ppm
2015-09-15301235010.630 ppm
2015-10-27303144010.610 ppm
2015-11-12306468010.610 ppm
2015-12-03307853010.680 ppm