EWG's Tap Water Database — 2019 UPDATE



Williams Water Supply

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
201228.0 ppb4424.0 ppb - 33.0 ppb
201323.3 ppb4420.0 ppb - 27.0 ppb
201426.3 ppb4422.0 ppb - 30.0 ppb
201523.3 ppb4419.0 ppb - 27.0 ppb
201621.8 ppb4411.0 ppb - 27.0 ppb
201726.0 ppb4422.0 ppb - 29.0 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
2012-02-06188646624.0 ppb
2012-05-08190232026.0 ppb
2012-08-13192402229.0 ppb
2012-10-02193666333.0 ppb
2013-01-21195864120.0 ppb
2013-04-03197023223.0 ppb
2013-08-07199632227.0 ppb
2013-11-12201830223.0 ppb
2014-02-10203447122.0 ppb
2014-05-05204999023.0 ppb
2014-08-04206905130.0 ppb
2014-11-10209225030.0 ppb
2015-02-04OE21299124.0 ppb
2015-05-04OE23893523.0 ppb
2015-08-05OE27706627.0 ppb
2015-11-09OE31616019.0 ppb
2016-02-01OE34217723.0 ppb
2016-05-04OE37454011.0 ppb
2016-08-08OE41298526.0 ppb
2016-11-02OE44864727.0 ppb
2017-02-01OE47701222.0 ppb
2017-08-02OE54580128.0 ppb
2017-10-10OE57757425.0 ppb
2017-11-09OE58886829.0 ppb