EWG's Tap Water Database — 2019 UPDATE



City of Detroit

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
20120.850 ppm110.700 ppm - 0.850 ppm
20130.710 ppm110.580 ppm - 0.710 ppm
20140.690 ppm110.560 ppm - 0.690 ppm
20150.540 ppm110.450 ppm - 0.540 ppm
20160.570 ppm110.570 ppm
20170.660 ppm110.660 ppm - 0.670 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
2012-08-140.850 ppm*
2013-05-130.710 ppm*
2014-05-130.690 ppm*
2015-05-110.540 ppm*
2016-05-100.570 ppm*
2017-05-160.660 ppm*

* Sample result is taken from the system's CCR report.