EWG's Tap Water Database — 2021 UPDATE



Entranosa Water and Wastewater Co-op

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
20151.04 ppb220.870 ppb - 1.20 ppb
20160.815 ppb220.750 ppb - 0.880 ppb
20171.45 ppb221.30 ppb - 1.60 ppb
20180.950 ppb220.950 ppb
20190.625 ppb220.470 ppb - 0.780 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
2015-08-1220150232431.20 ppb
2015-08-1220150232420.870 ppb
2016-08-0520160225490.880 ppb
2016-08-0520160225480.750 ppb
2017-08-1520170235831.60 ppb
2017-08-1520170235821.30 ppb
2018-08-0920180222780.950 ppb
2018-08-0920180222790.950 ppb
2019-08-1920190231560.470 ppb
2019-08-1920190231570.780 ppb