Fluoride
Marin Municipal Water District
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
Samples exceeding legal limit (MCL)
Samples exceeding
health guidelines
Testing results - average by year
| Year | Average result | Samples taken | Detections | Range of results |
|---|---|---|---|---|
| 2013 | N/A | 0 | 0 | N/A |
| 2014 | 0.933 ppm | 12 | 12 | 0.880 ppm - 0.970 ppm |
| 2015 | 0.770 ppm | 12 | 12 | 0.670 ppm - 0.880 ppm |
| 2016 | 0.728 ppm | 12 | 12 | 0.590 ppm - 0.840 ppm |
| 2017 | 0.760 ppm | 12 | 12 | 0.670 ppm - 0.900 ppm |
| 2018 | 0.756 ppm | 12 | 12 | 0.700 ppm - 0.820 ppm |
| 2019 | 0.707 ppm | 12 | 12 | 0.620 ppm - 0.790 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 |
|---|---|---|
| 2014-02-03 | 7747-011-0850 | 0.880 ppm |
| 2014-02-03 | 7747-005-0845 | 0.970 ppm |
| 2014-02-03 | 7747-004-1140 | 0.950 ppm |
| 2014-05-05 | 7747-011-0915 | 0.890 ppm |
| 2014-05-05 | 7747-005-1200 | 0.900 ppm |
| 2014-05-05 | 7747-004-1125 | 0.970 ppm |
| 2014-08-04 | 7747-011-0940 | 0.960 ppm |
| 2014-08-04 | 7747-004-1155 | 0.940 ppm |
| 2014-08-05 | 7747-005-1320 | 0.900 ppm |
| 2014-11-03 | 7747-011-1240 | 0.970 ppm |
| 2014-11-03 | 7747-005-1230 | 0.940 ppm |
| 2014-11-03 | 7747-004-1350 | 0.920 ppm |
| 2015-02-02 | 7747-004-1310 | 0.820 ppm |
| 2015-02-02 | 7747-011-0750 | 0.880 ppm |
| 2015-02-04 | 7747-005-0845 | 0.860 ppm |
| 2015-05-04 | 7747-011-1325 | 0.670 ppm |
| 2015-05-04 | 7747-004-0945 | 0.700 ppm |
| 2015-05-04 | 7747-005-0815 | 0.730 ppm |
| 2015-08-03 | 7747-004-0945 | 0.770 ppm |
| 2015-08-03 | 7747-005-1320 | 0.780 ppm |
| 2015-08-03 | 7747-011-1205 | 0.710 ppm |
| 2015-11-02 | 7747-004-0920 | 0.760 ppm |
| 2015-11-02 | 7747-005-0810 | 0.820 ppm |
| 2015-11-02 | 7747-011-1155 | 0.740 ppm |
| 2016-02-01 | 7747-004-0850 | 0.730 ppm |
| 2016-02-01 | 7747-011-1205 | 0.660 ppm |
| 2016-02-02 | 7747-005-1035 | 0.770 ppm |
| 2016-05-02 | 7747-011-0840 | 0.740 ppm |
| 2016-05-02 | 7747-004-1045 | 0.730 ppm |
| 2016-05-02 | 7747-005-0840 | 0.840 ppm |
| 2016-08-01 | 7747-004-0845 | 0.710 ppm |
| 2016-08-01 | 7747-011-1145 | 0.590 ppm |
| 2016-08-01 | 7747-005-0800 | 0.760 ppm |
| 2016-11-07 | 7747-004-0925 | 0.700 ppm |
| 2016-11-07 | 7747-011-1150 | 0.760 ppm |
| 2016-11-07 | 7747-005-0705 | 0.740 ppm |
| 2017-02-06 | 7747-004-1015 | 0.750 ppm |
| 2017-02-06 | 7747-011-0755 | 0.800 ppm |
| 2017-02-06 | 7747-005-1035 | 0.820 ppm |
| 2017-05-01 | 7747-005-0800 | 0.900 ppm |
| 2017-05-01 | 7747-004-1150 | 0.820 ppm |
| 2017-05-01 | 7747-011-0750 | 0.810 ppm |
| 2017-08-07 | 7747-005-0800 | 0.760 ppm |
| 2017-08-07 | 7747-004-1140 | 0.690 ppm |
| 2017-08-07 | 7747-011-0900 | 0.670 ppm |
| 2017-11-06 | 7747-004-1200 | 0.680 ppm |
| 2017-11-06 | 7747-011-0920 | 0.680 ppm |
| 2017-11-06 | 7747-005-0930 | 0.740 ppm |
| 2018-02-07 | 7747-004-1105 | 0.700 ppm |
| 2018-02-07 | 7747-011-0945 | 0.730 ppm |
| 2018-02-07 | 7747-005-1245 | 0.730 ppm |
| 2018-05-07 | 7747-005-0800 | 0.770 ppm |
| 2018-05-07 | 7747-004-0905 | 0.760 ppm |
| 2018-05-07 | 7747-011-0920 | 0.710 ppm |
| 2018-08-06 | 7747-004-0915 | 0.760 ppm |
| 2018-08-06 | 7747-005-0810 | 0.820 ppm |
| 2018-08-06 | 7747-011-1045 | 0.750 ppm |
| 2018-11-05 | 7747-011-1045 | 0.790 ppm |
| 2018-11-05 | 7747-005-0940 | 0.780 ppm |
| 2018-11-05 | 7747-004-0845 | 0.770 ppm |
| 2019-02-04 | 7747-011-1135 | 0.770 ppm |
| 2019-02-04 | 7747-004-1045 | 0.690 ppm |
| 2019-02-04 | 7747-005-0930 | 0.680 ppm |
| 2019-05-06 | 7747-011-0910 | 0.710 ppm |
| 2019-05-06 | 7747-005-0730 | 0.660 ppm |
| 2019-05-09 | 7747-004-1050 | 0.680 ppm |
| 2019-08-05 | 7747-011-0845 | 0.670 ppm |
| 2019-08-05 | 7747-004-1250 | 0.790 ppm |
| 2019-08-05 | 7747-005-0730 | 0.720 ppm |
| 2019-11-04 | 7747-011-0810 | 0.720 ppm |
| 2019-11-04 | 7747-005-0730 | 0.620 ppm |
| 2019-11-04 | 7747-004-1240 | 0.770 ppm |