EWG's Tap Water Database — 2021 UPDATE



Ponderosa Basin Mutual Water Company

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
20160.536 ppm76ND - 0.730 ppm
20170.710 ppm110.710 ppm
20190.583 ppm660.510 ppm - 0.700 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
2016-11-295802-007-11300.530 ppm
2016-11-295802-009-10300.590 ppm
2016-11-295802-010-10000.610 ppm
2016-11-295802-011-09150.610 ppm
2016-11-295802-012-08300.730 ppm
2016-11-295802-014-08000.680 ppm
2017-12-185802-007-09200.710 ppm
2019-10-225802-007-12000.600 ppm
2019-10-225802-009-12300.580 ppm
2019-10-225802-010-13000.700 ppm
2019-10-225802-011-13300.550 ppm
2019-10-225802-012-14000.560 ppm
2019-10-225802-014-14300.510 ppm