EWG's Tap Water Database — 2019 UPDATE



Lake Mills Waterworks

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
20131.57 ppb330.820 ppb - 2.30 ppb
20140.987 ppb330.260 ppb - 2.10 ppb
20151.12 ppb220.430 ppb - 1.80 ppb
20164.90 ppb114.90 ppb
20171.37 ppb330.280 ppb - 3.40 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
2013-08-207392460.820 ppb
2013-08-207392471.60 ppb
2013-08-207392452.30 ppb
2014-09-108182730.260 ppb
2014-09-108182750.600 ppb
2014-09-158185542.10 ppb
2015-04-158545640.430 ppb
2015-07-158712861.80 ppb
2016-08-089378854.90 ppb
2017-03-089767290.280 ppb
2017-03-089767260.440 ppb
2017-08-0910103453.40 ppb