EWG's Tap Water Database — 2021 UPDATE



Hillside Village

Chloroform, one of the total trihalomethanes (TTHMs), is formed when chlorine or other disinfectants are used to treat drinking water. Chloroform and other disinfection byproducts increase the risk of cancer and may cause problems during pregnancy. Read More.

In addition to tap water disinfection, chloroform pollution in the environment also comes from industrial discharges from pulp and paper mills, and from urban wastewater effluent. Human studies show that chloroform damages the kidneys, liver and central nervous system. In animals, chloroform causes infertility, birth defects and cancer.

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
20150.1000 ppb110.1000 ppb
20160.200 ppb110.200 ppb
20170.300 ppb110.300 ppb
20180.1000 ppb220.1000 ppb
20190.400 ppb110.400 ppb

ppb = parts per billion

State and national drinking water standards and health guidelines

EWG Health Guideline 0.4 ppb

The EWG Health Guideline of 0.4 ppb for chloroform 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
2015-09-22L5771669-10.1000 ppb
2016-08-16L6370543-10.200 ppb
2017-08-11L6914570-10.300 ppb
2018-08-13L7053842-10.1000 ppb
2018-09-05L7063121-10.1000 ppb
2019-08-13L7145911-10.400 ppb