EWG's Tap Water Database



Danville City Water Works

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
20100.810 ppm110.810 ppm
20111.14 ppm221.08 ppm - 1.19 ppm
20120.635 ppm220.630 ppm - 0.640 ppm
20131.03 ppm221.02 ppm - 1.03 ppm
20140.845 ppm220.820 ppm - 0.870 ppm
20151.10 ppm221.10 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
2010-02-16906787010.810 ppm
2011-02-08913470011.08 ppm
2011-02-08913471011.19 ppm
2012-02-06921010010.630 ppm
2012-02-06921011010.640 ppm
2013-02-18928997011.02 ppm
2013-02-18928998011.03 ppm
2014-02-17934843010.870 ppm
2014-02-17934845010.820 ppm
2015-03-02941913011.10 ppm
2015-03-02941912011.10 ppm