EWG's Tap Water Database — 2019 UPDATE



Centennial Water and Sanitation 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
20120.867 ppm330.770 ppm - 0.950 ppm
20130.810 ppm330.770 ppm - 0.890 ppm
20140.780 ppm220.770 ppm - 0.790 ppm
20150.835 ppm220.780 ppm - 0.890 ppm
20161.00 ppm330.920 ppm - 1.07 ppm
20170.887 ppm330.860 ppm - 0.940 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 Result
2012-08-220.880 ppm
2012-08-230.950 ppm
2012-10-310.770 ppm
2013-03-190.770 ppm
2013-03-190.890 ppm
2013-08-270.770 ppm
2014-07-230.770 ppm
2014-07-290.790 ppm
2015-07-270.780 ppm
2015-08-120.890 ppm
2016-07-270.920 ppm
2016-07-271.02 ppm
2016-08-171.07 ppm
2017-01-250.860 ppm
2017-01-250.940 ppm
2017-08-150.860 ppm