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EWG's Tap Water Database — 2019 UPDATE

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Total trihalomethanes (TTHMs)

Holden Water Division, DPW

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.

The health guideline of 0.15 parts per billion, or ppb, for the group of four trihalomethanes, or THM4/TTHM, was defined in a peer-reviewed scientific study by EWG and represents a one-in-one-million lifetime cancer risk level.

Click here to read more about disinfection byproducts.

 

111

Samples

8

Samples exceeding legal limit (MCL)

94

Samples exceeding
health guidelines

Testing results - average by year

 
YearAverage resultSamples takenDetectionsRange of results
2012ND50ND
2013ND40ND
2014ND40ND
201537.7 ppb3230ND - 97.0 ppb
201641.5 ppb3432ND - 110.0 ppb
201737.2 ppb32327.73 ppb - 85.4 ppb

ppb = parts per billion

State and national drinking water standards and health guidelines

EWG Health Guideline 0.15 ppb

The health guideline of 0.15 parts per billion, or ppb, for the group of four trihalomethanes, or THM4/TTHM, was defined in a peer-reviewed scientific study by EWG and represents a one-in-one-million lifetime cancer risk level.

EPA Maximum Contaminant
Level (MCL) 80 ppb

The legal limit for the group of four trihalomethanes, established in 1998, was based on the need for residual disinfectant levels in water served to customers and the cost of treatment. This limit does not fully protect against the risk of cancer due to exposure to trihalomethanes.

ppb = parts per billion

All test results

Date Result
2012-01-05ND
2012-05-08ND
2012-06-11ND
2012-08-22ND
2012-11-20ND
2013-02-20ND
2013-05-16ND
2013-08-21ND
2013-11-18ND
2014-02-18ND
2014-05-20ND
2014-08-20ND
2014-11-19ND
2015-02-1826.0 ppb
2015-02-1826.0 ppb
2015-02-18ND
2015-02-18ND
2015-02-1826.0 ppb
2015-02-1826.0 ppb
2015-02-1823.0 ppb
2015-02-1823.0 ppb
2015-05-1931.0 ppb
2015-05-1931.0 ppb
2015-05-1924.0 ppb
2015-05-1924.0 ppb
2015-05-1931.0 ppb
2015-05-1931.0 ppb
2015-05-1924.0 ppb
2015-05-1924.0 ppb
2015-08-1876.0 ppb
2015-08-1876.0 ppb
2015-08-1871.0 ppb
2015-08-1871.0 ppb
2015-08-1897.0 ppb
2015-08-1897.0 ppb
2015-08-1851.0 ppb
2015-08-1851.0 ppb
2015-11-1718.0 ppb
2015-11-1718.0 ppb
2015-11-1711.0 ppb
2015-11-1711.0 ppb
2015-11-1770.0 ppb
2015-11-1770.0 ppb
2015-11-1724.0 ppb
2015-11-1724.0 ppb
2016-02-02ND
2016-02-1627.0 ppb
2016-02-1627.0 ppb
2016-02-1622.0 ppb
2016-02-1622.0 ppb
2016-02-1649.0 ppb
2016-02-1649.0 ppb
2016-02-1623.0 ppb
2016-02-1623.0 ppb
2016-05-1739.0 ppb
2016-05-1739.0 ppb
2016-05-1713.0 ppb
2016-05-1713.0 ppb
2016-05-1760.0 ppb
2016-05-1760.0 ppb
2016-05-1739.0 ppb
2016-05-1739.0 ppb
2016-08-1684.0 ppb
2016-08-1684.0 ppb
2016-08-1678.0 ppb
2016-08-1678.0 ppb
2016-08-16110.0 ppb
2016-08-16110.0 ppb
2016-08-1649.0 ppb
2016-08-1649.0 ppb
2016-09-06ND
2016-11-1536.7 ppb
2016-11-1536.7 ppb
2016-11-159.08 ppb
2016-11-159.08 ppb
2016-11-1549.6 ppb
2016-11-1549.6 ppb
2016-11-1516.5 ppb
2016-11-1516.5 ppb
2017-02-2118.1 ppb
2017-02-2118.1 ppb
2017-02-2113.5 ppb
2017-02-2113.5 ppb
2017-02-2121.3 ppb
2017-02-2121.3 ppb
2017-02-2126.9 ppb
2017-02-2126.9 ppb
2017-05-1647.7 ppb
2017-05-1647.7 ppb
2017-05-1630.1 ppb
2017-05-1630.1 ppb
2017-05-1636.6 ppb
2017-05-1636.6 ppb
2017-05-1642.0 ppb
2017-05-1642.0 ppb
2017-08-1562.1 ppb
2017-08-1562.1 ppb
2017-08-1585.4 ppb
2017-08-1585.4 ppb
2017-08-1549.9 ppb
2017-08-1549.9 ppb
2017-08-1667.0 ppb
2017-08-1667.0 ppb
2017-11-218.32 ppb
2017-11-218.32 ppb
2017-11-217.73 ppb
2017-11-217.73 ppb
2017-11-2147.7 ppb
2017-11-2147.7 ppb
2017-11-2131.0 ppb
2017-11-2131.0 ppb