EWG's Tap Water Database — 2019 UPDATE



San Gabriel County WD

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
20120.816 ppm770.600 ppm - 0.920 ppm
20130.830 ppm110.830 ppm
20140.713 ppm440.590 ppm - 0.880 ppm
20150.753 ppm440.690 ppm - 0.830 ppm
20160.630 ppm110.630 ppm
20170.796 ppm550.700 ppm - 0.850 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
2012-06-043761-001-08450.600 ppm
2012-06-043761-007-11000.890 ppm
2012-06-043761-011-08300.720 ppm
2012-06-043761-010-11300.920 ppm
2012-06-043761-009-11500.860 ppm
2012-07-179588-007-09450.840 ppm
2012-07-179588-009-09150.880 ppm
2013-05-243761-020-11250.830 ppm
2014-06-173761-020-10200.770 ppm
2014-07-149588-011-09450.610 ppm
2014-09-259588-001-09150.590 ppm
2014-10-089588-010-09200.880 ppm
2015-06-113761-007-09050.770 ppm
2015-06-113761-010-08450.830 ppm
2015-06-113761-011-08000.720 ppm
2015-07-169588-007-09200.690 ppm
2016-07-189588-009-09250.630 ppm
2017-04-139588-020-09400.850 ppm
2017-06-083761-020-10300.840 ppm
2017-07-179588-011-09450.700 ppm
2017-10-189588-010-09100.800 ppm
2017-10-263761-009-10000.790 ppm