EWG's Tap Water Database — 2019 UPDATE



California Water Service Company - Dominguez

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
20120.494 ppm16160.250 ppm - 0.910 ppm
20130.243 ppm65ND - 0.450 ppm
20140.255 ppm220.200 ppm - 0.310 ppm
20150.280 ppm110.280 ppm
20160.238 ppm65ND - 0.400 ppm
20170.396 ppm550.210 ppm - 0.580 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
2012-01-105810-031-10350.880 ppm
2012-01-105810-031-11000.430 ppm
2012-02-025810-031-10470.880 ppm
2012-02-025810-031-10570.370 ppm
2012-03-085810-031-10380.910 ppm
2012-03-085810-031-10470.290 ppm
2012-04-055810-031-10370.660 ppm
2012-04-055810-031-10460.250 ppm
2012-05-105810-031-10490.360 ppm
2012-06-195810-031-11000.370 ppm
2012-07-265810-031-10470.450 ppm
2012-08-095810-031-12580.450 ppm
2012-08-205810-018-11240.310 ppm
2012-10-055810-031-12450.520 ppm
2012-11-145810-031-14330.380 ppm
2012-12-055810-031-14130.390 ppm
2013-03-135810-024-10470.240 ppm
2013-05-085810-036-11430.450 ppm
2013-06-185810-023-13120.240 ppm
2013-09-195810-004-14300.330 ppm
2013-10-165810-022-14000.200 ppm
2014-08-275810-016-13100.310 ppm
2014-10-085810-019-10220.200 ppm
2015-03-259590-018-13550.280 ppm
2016-01-135810-023-13200.190 ppm
2016-03-239590-018-13400.280 ppm
2016-05-115810-036-11400.400 ppm
2016-09-075810-004-13000.320 ppm
2016-12-289590-019-09300.240 ppm
2017-03-089590-019-14300.580 ppm
2017-08-235810-019-11000.210 ppm
2017-08-235810-016-12120.520 ppm
2017-10-119590-036-13350.450 ppm
2017-12-265810-024-13150.220 ppm