EWG's Tap Water Database


Total trihalomethanes (TTHMs)

City of Federal Heights

Trihalomethanes are cancer-causing contaminants that form during water treatment with chlorine and other disinfectants. The total trihalomethanes group includes four chemicals: chloroform, bromodichloromethane, dibromochloromethane and bromoform. Read More.

Studies conducted in the U.S. and Europe have found that drinking tap water that carries disinfection byproducts increases the risk of developing bladder cancer. In animal studies, all trihalomethanes cause liver, kidney and intestinal tumors. Some human epidemiological studies also reported an association between disinfection byproducts and an increased risk of problems during pregnancy, including spontaneous miscarriage, cardiovascular defects, neural tube defects and low birth weight.

In 2010, the California Office of Environmental Health Hazard Assessment published a draft public health goal for the trihalomethanes group at 0.8 parts per billion, or 100 times lower than the federal legal limit of 80 parts per billion for this contaminant group.

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
201027.1 ppb8819.6 ppb - 37.9 ppb
201130.5 ppb8816.9 ppb - 51.3 ppb
201225.6 ppb8820.8 ppb - 37.1 ppb
201331.1 ppb8821.0 ppb - 50.1 ppb
201430.0 ppb8820.6 ppb - 39.5 ppb
201527.1 ppb8822.6 ppb - 29.4 ppb

ppb = parts per billion.

State and national drinking water standards and health guidelines

Health Guideline 0.15 ppb

The health guideline of 0.15 ppb for trihalomethanes was defined by in a peer-reviewed scientific study by EWG and represents a one-in-one-million lifetime cancer risk level. as a draft public health goal, the level of drinking water contaminant that does not pose a significant health risk. This health guideline protects against cancer.

ppb = parts per billion.

EPA Maximum Contaminant
Level (MCL) 80 ppb

The enforceable federal standard that defines the highest level of a contaminant allowed in drinking water.

ppb = parts per billion.

All test results

Date Result
2010-03-2523.4 ppb
2010-03-2521.6 ppb
2010-06-1726.7 ppb
2010-06-1729.9 ppb
2010-09-2337.9 ppb
2010-09-2333.5 ppb
2010-12-1519.6 ppb
2010-12-1524.2 ppb
2011-03-1726.2 ppb
2011-03-1722.9 ppb
2011-06-2231.3 ppb
2011-06-2230.6 ppb
2011-09-2246.8 ppb
2011-09-2251.3 ppb
2011-12-0817.9 ppb
2011-12-0816.9 ppb
2012-03-2123.1 ppb
2012-03-2120.9 ppb
2012-06-2125.3 ppb
2012-06-2124.3 ppb
2012-09-1837.1 ppb
2012-09-1832.5 ppb
2012-12-1120.8 ppb
2012-12-1121.1 ppb
2013-03-2121.0 ppb
2013-03-2123.0 ppb
2013-06-2030.4 ppb
2013-06-2028.2 ppb
2013-09-2345.4 ppb
2013-09-2350.1 ppb
2013-12-1624.6 ppb
2013-12-1626.4 ppb
2014-03-2420.6 ppb
2014-03-2423.6 ppb
2014-06-1829.3 ppb
2014-06-1829.9 ppb
2014-09-2538.8 ppb
2014-09-2539.5 ppb
2014-12-1731.1 ppb
2014-12-1726.8 ppb
2015-03-1122.6 ppb
2015-03-1123.3 ppb
2015-06-1027.8 ppb
2015-06-1027.9 ppb
2015-09-1028.8 ppb
2015-09-1029.1 ppb
2015-12-0829.4 ppb
2015-12-0827.7 ppb