EWG's Tap Water Database — 2019 UPDATE



San Francisco Regional Water System

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
20120.603 ppm330.150 ppm - 0.890 ppm
20130.585 ppm440.340 ppm - 0.830 ppm
20140.740 ppm330.470 ppm - 0.900 ppm
20150.602 ppm330.475 ppm - 0.710 ppm
20160.609 ppm330.448 ppm - 0.718 ppm
20170.523 ppm330.305 ppm - 0.680 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
2012-06-139553-015-12200.150 ppm
2012-06-139553-001-10450.890 ppm
2012-07-249553-016-09150.770 ppm
2013-06-189553-016-09360.800 ppm
2013-06-189553-001-11100.830 ppm
2013-10-079590-015-10240.370 ppm
2013-10-079553-015-10240.340 ppm
2014-06-179553-016-09040.850 ppm
2014-06-179553-001-11300.900 ppm
2014-09-169553-015-10350.470 ppm
2015-05-279553-016-08300.710 ppm
2015-05-279553-001-12350.620 ppm
2015-06-189553-015-09150.475 ppm
2016-06-149553-015-12310.448 ppm
2016-06-149553-001-11050.718 ppm
2016-06-219553-016-10550.660 ppm
2017-06-199553-016-09530.584 ppm
2017-06-199553-015-11000.305 ppm
2017-06-199553-001-10250.680 ppm