EWG's Tap Water Database — 2019 UPDATE



Golden State Water Company (GSWC) - San Dimas

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
20120.760 ppm220.730 ppm - 0.790 ppm
20130.658 ppm13130.450 ppm - 0.780 ppm
20140.420 ppm110.420 ppm
20150.595 ppm220.560 ppm - 0.630 ppm
20160.624 ppm990.400 ppm - 0.770 ppm
20170.613 ppm330.510 ppm - 0.670 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
2012-08-142706-014-10440.730 ppm
2012-08-159588-014-09450.790 ppm
2013-02-209588-017-09550.490 ppm
2013-03-112706-039-14030.450 ppm
2013-04-092706-039-13120.490 ppm
2013-05-149588-005-09400.780 ppm
2013-05-149588-004-10050.740 ppm
2013-05-149588-003-10250.680 ppm
2013-05-222706-005-10250.780 ppm
2013-05-222706-004-10330.750 ppm
2013-05-222706-003-10170.660 ppm
2013-05-312706-013-14030.700 ppm
2013-06-279588-013-09450.740 ppm
2013-11-149588-051-09200.640 ppm
2013-11-192706-051-13510.650 ppm
2014-02-192706-017-09420.420 ppm
2015-09-112706-014-09150.630 ppm
2015-09-119588-014-09050.560 ppm
2016-03-039588-017-08150.400 ppm
2016-05-129588-005-11100.670 ppm
2016-05-129588-004-11000.500 ppm
2016-05-129588-003-09100.590 ppm
2016-06-212706-005-09420.770 ppm
2016-06-212706-004-09480.650 ppm
2016-06-212706-003-10150.680 ppm
2016-09-132706-013-11470.770 ppm
2016-09-149588-013-09000.590 ppm
2017-01-059588-051-08000.670 ppm
2017-01-119590-051-09050.660 ppm
2017-02-239590-017-10500.510 ppm