EWG's Tap Water Database — 2019 UPDATE



City of Portsmouth

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
20120.950 ppm12120.750 ppm - 1.27 ppm
20130.974 ppm13130.790 ppm - 1.11 ppm
20141.04 ppm12120.780 ppm - 1.19 ppm
20150.918 ppm12120.630 ppm - 1.27 ppm
20160.712 ppm13130.610 ppm - 0.790 ppm
20170.759 ppm11110.600 ppm - 1.12 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
2012-01-0312-00060FLS1.16 ppm
2012-02-0112-01774FLS0.940 ppm
2012-03-0612-03600FLS0.780 ppm
2012-04-1112-05479IOCA1.27 ppm
2012-04-1212-06193FLS0.960 ppm
2012-05-0812-07774FLS0.980 ppm
2012-07-1612-11028FLS0.750 ppm
2012-08-1012-13218FLS0.780 ppm
2012-09-1512-15194FLS0.770 ppm
2012-10-0512-16504FLS1.01 ppm
2012-11-0812-18187FLS0.950 ppm
2012-12-0312-19189FLS1.05 ppm
2013-01-0213-00746FLS0.990 ppm
2013-02-0413-02165FLS1.04 ppm
2013-03-0513-04598FLS0.840 ppm
2013-04-0313-05585FLS1.11 ppm
2013-04-0813-05584IOC0.870 ppm
2013-05-0713-07734FLS1.05 ppm
2013-06-0313-08794FLS1.07 ppm
2013-07-0213-11281FLS1.000 ppm
2013-07-0613-12790FLS1.06 ppm
2013-09-0613-14743FLS1.02 ppm
2013-10-0113-15776FLS0.970 ppm
2013-11-0713-17724FLS0.850 ppm
2013-12-1113-19171FLS0.790 ppm
2014-01-2814-01227FLS1.11 ppm
2014-02-0714-02776FLS0.930 ppm
2014-03-0614-03770FLS1.19 ppm
2014-04-0214-05026IOC1.19 ppm
2014-04-2114-060411.04 ppm
2014-05-0614-068551.04 ppm
2014-06-0914-089271.16 ppm
2014-07-0114-101191.04 ppm
2014-08-0614-118470.780 ppm
2014-10-1414-162671.06 ppm
2014-11-0514-180200.950 ppm
2014-12-0514-194290.980 ppm
2015-01-20460013-JAMES R.1.12 ppm
2015-02-13460013-JAMES R.0.630 ppm
2015-03-06460013-JAMES R.1.27 ppm
2015-04-06460013-JAMES R.0.710 ppm
2015-04-18460013-JAMES R.0.760 ppm
2015-05-08460013-JAMES R.0.860 ppm
2015-06-16460013-JAMES R.1.03 ppm
2015-07-09460013-JAMES R.1.17 ppm
2015-08-13460013-JAMES R.0.870 ppm
2015-10-07460013-JAMES R.1.10 ppm
2015-11-18460013-JAMES R.0.750 ppm
2015-12-18460013-JAMES R.0.750 ppm
2016-01-1816-010410.700 ppm
2016-02-0216-014920.700 ppm
2016-03-1016-051220.610 ppm
2016-04-0816-065840.760 ppm
2016-04-1816-06585-INO0.770 ppm
2016-05-0616-090190.790 ppm
2016-06-1116-108650.700 ppm
2016-07-1316-125420.720 ppm
2016-08-0316-138080.740 ppm
2016-09-2016-169560.700 ppm
2016-10-2016-188990.730 ppm
2016-11-1716-209000.680 ppm
2016-12-2016-229170.660 ppm
2017-01-0417-002401.12 ppm
2017-02-0117-017930.600 ppm
2017-03-0217-037380.720 ppm
2017-04-1217-066560.710 ppm
2017-05-0117-076040.740 ppm
2017-06-0317-107710.750 ppm
2017-07-1817-127490.740 ppm
2017-09-0617-172860.690 ppm
2017-10-0217-189500.680 ppm
2017-11-0217-216370.740 ppm
2017-12-0317-234730.860 ppm