EWG's Tap Water Database — 2021 UPDATE



Thomas Hill PWSD 1

Dibromochloromethane, one of the total trihalomethanes (TTHMs), is formed when chlorine or other disinfectants are used to treat drinking water. Dibromochloromethane and other disinfection byproducts increase the risk of cancer and may cause problems during pregnancy. Click here to read more about disinfection byproducts.





Samples exceeding legal limit (MCL)


Samples exceeding
health guidelines

Testing results - average by year

YearAverage resultSamples takenDetectionsRange of results
20140.961 ppb86ND - 1.68 ppb
20151.79 ppb880.650 ppb - 2.56 ppb
20161.56 ppb881.04 ppb - 2.84 ppb
20171.35 ppb880.690 ppb - 1.94 ppb
20181.49 ppb880.560 ppb - 3.58 ppb
20190.864 ppb87ND - 1.37 ppb

ppb = parts per billion

State and national drinking water standards and health guidelines

EWG Health Guideline 0.1 ppb

The EWG Health Guideline of 0.1 ppb for dibromochloromethane was proposed in 2018 by the California Office of Environmental Health Hazard Assessment as a one-in-a-million lifetime risk of cancer. Values greater than one-in-a-million cancer risk level can result in increased cancer cases above one in a million people.

ppb = parts per billion

All test results

Date Lab ID Result
2014-02-13AC181561.30 ppb
2014-02-13AC181551.24 ppb
2014-05-21AC231630.900 ppb
2014-05-21AC231640.910 ppb
2014-08-21AC332301.66 ppb
2014-08-21AC332311.68 ppb
2015-02-19AC419351.08 ppb
2015-02-19AC419360.650 ppb
2015-05-26AC465112.47 ppb
2015-05-26AC465122.30 ppb
2015-08-20AC573601.27 ppb
2015-08-20AC573591.44 ppb
2015-11-23AC627772.52 ppb
2015-11-23AC627782.56 ppb
2016-02-24AC663221.05 ppb
2016-02-24AC663211.04 ppb
2016-05-24AC720152.84 ppb
2016-05-24AC720142.61 ppb
2016-08-17AC816141.09 ppb
2016-08-17AC816151.14 ppb
2016-11-17AC869131.34 ppb
2016-11-17AC869141.36 ppb
2017-03-06AC927841.80 ppb
2017-03-06AC927851.94 ppb
2017-05-17AC957480.690 ppb
2017-05-17AC957490.790 ppb
2017-08-14AD033371.32 ppb
2017-08-14AD033361.38 ppb
2017-11-28AD094631.43 ppb
2017-11-28AD094621.41 ppb
2018-03-20AD176850.680 ppb
2018-03-20AD176860.600 ppb
2018-05-16AD204811.52 ppb
2018-05-16AD204821.56 ppb
2018-08-13AD311562.81 ppb
2018-08-13AD311573.58 ppb
2018-11-19AD356910.560 ppb
2018-11-19AD356920.570 ppb
2019-02-21AD393600.580 ppb
2019-05-21AD474400.890 ppb
2019-05-21AD474410.890 ppb
2019-08-19AD538811.37 ppb
2019-08-19AD538821.36 ppb
2019-12-03AD580670.880 ppb
2019-12-03AD580660.940 ppb