EWG's Tap Water Database — 2019 UPDATE



City of Denison

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
20120.1000 ppm110.1000 ppm
20130.224 ppm220.207 ppm - 0.240 ppm
20140.282 ppm220.209 ppm - 0.355 ppm
20150.269 ppm220.225 ppm - 0.312 ppm
20160.135 ppm220.127 ppm - 0.142 ppm
20170.357 ppm220.286 ppm - 0.428 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
2012-02-0112020400020.1000 ppm
2013-03-0613032630020.240 ppm
2013-06-12Q13022050130.207 ppm
2014-02-25Q14060590160.355 ppm
2014-02-25Q14060590150.209 ppm
2015-03-03Q15078940020.312 ppm
2015-06-15Q15220520050.225 ppm
2016-02-16Q16067680110.142 ppm
2016-02-16Q16067680090.127 ppm
2017-02-07Q17054660050.286 ppm
2017-08-08Q17337900050.428 ppm