EWG's Tap Water Database — 2019 UPDATE



City of Houston

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
20120.286 ppm12120.220 ppm - 0.500 ppm
20130.413 ppm18180.210 ppm - 0.660 ppm
20140.265 ppm3534ND - 0.430 ppm
20150.254 ppm1211ND - 0.360 ppm
20160.326 ppm1817ND - 0.760 ppm
20170.306 ppm3332ND - 0.510 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
2012-01-31AB796930.220 ppm
2012-01-31AB796910.250 ppm
2012-01-31AB796900.260 ppm
2012-01-31AB796890.260 ppm
2012-01-31AB796920.240 ppm
2012-01-31AB796940.230 ppm
2012-02-01AB796820.330 ppm
2012-02-01AB796810.380 ppm
2012-02-01AB796800.280 ppm
2012-02-01AB796830.500 ppm
2012-04-10AB863750.250 ppm
2012-07-24AB960290.230 ppm
2013-02-25AC115010.370 ppm
2013-02-25AC115050.550 ppm
2013-02-25AC115020.590 ppm
2013-02-25AC114970.360 ppm
2013-02-25AC115000.360 ppm
2013-02-26AC116760.400 ppm
2013-03-11AC128460.460 ppm
2013-03-11AC128440.450 ppm
2013-03-11AC128420.510 ppm
2013-03-11AC128450.580 ppm
2013-09-24AC310830.470 ppm
2013-10-24AC331700.280 ppm
2013-10-24AC331710.420 ppm
2013-10-24AC331680.270 ppm
2013-10-24AC331690.210 ppm
2013-10-29AC335770.280 ppm
2013-11-04AC339750.660 ppm
2013-12-17AC377350.220 ppm
2014-02-03AC409940.290 ppm
2014-03-14AC470390.240 ppm
2014-03-14AC470380.260 ppm
2014-03-14AC470370.250 ppm
2014-04-16AC507230.270 ppm
2014-04-16AC507240.280 ppm
2014-04-16AC507340.290 ppm
2014-04-17AC509930.240 ppm
2014-04-17AC509900.280 ppm
2014-04-17AC509910.190 ppm
2014-04-17AC509940.190 ppm
2014-04-17AC509920.310 ppm
2014-04-17AC509950.310 ppm
2014-04-17AC509960.190 ppm
2014-04-17AC509970.200 ppm
2014-06-03AC557550.410 ppm
2014-06-03AC557540.230 ppm
2014-06-03AC557530.160 ppm
2014-06-03AC557500.430 ppm
2014-07-15AC596590.340 ppm
2014-07-15AC596600.320 ppm
2014-07-16AC597950.330 ppm
2014-08-14AC636050.400 ppm
2014-10-08AC691050.210 ppm
2014-10-08AC691060.220 ppm
2014-10-08AC691070.270 ppm
2014-10-09AC693130.350 ppm
2014-10-09AC693150.200 ppm
2014-10-09AC693160.200 ppm
2014-12-09AC741160.260 ppm
2014-12-09AC741150.250 ppm
2014-12-09AC741140.260 ppm
2014-12-18AC754000.340 ppm
2014-12-18AC754010.310 ppm
2015-03-04AC827860.310 ppm
2015-03-05AC827980.310 ppm
2015-06-04AC945520.260 ppm
2015-06-04AC945530.180 ppm
2015-06-04AC945540.340 ppm
2015-07-21AD002950.230 ppm
2015-07-21AD002970.360 ppm
2015-07-21AD002940.290 ppm
2015-07-21AD002960.230 ppm
2015-09-17AD074880.260 ppm
2015-11-12AD132920.280 ppm
2016-02-18AD241620.350 ppm
2016-03-03AD268010.180 ppm
2016-03-16AD289480.190 ppm
2016-03-16AD289470.190 ppm
2016-03-17AD292770.520 ppm
2016-03-17AD292760.230 ppm
2016-03-23AD300350.210 ppm
2016-03-23AD300370.310 ppm
2016-09-20AD502620.350 ppm
2016-09-20AD502630.530 ppm
2016-09-21AD506270.430 ppm
2016-10-06AD526120.260 ppm
2016-10-06AD526090.430 ppm
2016-10-06AD526100.260 ppm
2016-10-06AD526110.200 ppm
2016-10-06AD526130.470 ppm
2016-11-21AD587150.760 ppm
2017-01-26AD669880.220 ppm
2017-01-26AD669860.220 ppm
2017-01-26AD669850.410 ppm
2017-02-28AD723140.480 ppm
2017-02-28AD723190.280 ppm
2017-03-01AD726600.450 ppm
2017-03-01AD726590.440 ppm
2017-03-02AD729530.460 ppm
2017-03-28AD770330.200 ppm
2017-03-28AD770340.230 ppm
2017-03-28AD770360.200 ppm
2017-03-28AD770350.460 ppm
2017-03-29AD773220.410 ppm
2017-03-29AD773360.460 ppm
2017-04-26AD810690.500 ppm
2017-04-27AD813690.220 ppm
2017-07-06AD884010.340 ppm
2017-07-06AD884020.230 ppm
2017-07-06AD884030.170 ppm
2017-07-25AD904550.380 ppm
2017-09-11AD953350.270 ppm
2017-09-11AD953370.410 ppm
2017-09-11AD953360.220 ppm
2017-09-26AD978960.510 ppm
2017-09-26AD978940.230 ppm
2017-09-26AD978930.200 ppm
2017-09-26AD978950.210 ppm
2017-11-07AE037600.310 ppm
2017-11-07AE037620.260 ppm
2017-11-07AE037610.280 ppm
2017-11-07AE037640.200 ppm
2017-11-07AE037630.230 ppm