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EWG's Tap Water Database — 2021 UPDATE

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Total trihalomethanes (TTHMs)

San Gabriel County WD

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.

MORE ABOUT THIS CONTAMINANT

 

96

Samples

0

Samples exceeding legal limit (MCL)

74

Samples exceeding
health guidelines

Testing results - average by year

 
YearAverage resultSamples takenDetectionsRange of results
20145.03 ppb1612ND - 15.0 ppb
20154.36 ppb1614ND - 11.0 ppb
20162.53 ppb169ND - 8.00 ppb
20171.98 ppb1611ND - 4.90 ppb
20182.65 ppb1613ND - 5.50 ppb
20193.25 ppb1615ND - 5.60 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 Lab ID Result
2014-01-239588-802-0845ND
2014-01-239588-800-0900ND
2014-01-239588-801-13008.50 ppb
2014-01-239588-803-12258.40 ppb
2014-04-229588-803-10459.00 ppb
2014-04-229588-802-0830ND
2014-04-229588-801-120010.00 ppb
2014-04-229588-800-08402.80 ppb
2014-07-239588-803-09056.70 ppb
2014-07-239588-802-0830ND
2014-07-239588-801-08457.40 ppb
2014-07-239588-800-08202.40 ppb
2014-10-239588-802-08500.540 ppb
2014-10-239588-801-12158.20 ppb
2014-10-239588-803-120015.0 ppb
2014-10-239588-800-09051.50 ppb
2015-01-239588-803-11308.80 ppb
2015-01-239588-802-0820ND
2015-01-239588-801-120511.0 ppb
2015-01-239588-800-08301.50 ppb
2015-04-229588-803-11202.50 ppb
2015-04-229588-802-08154.30 ppb
2015-04-229588-800-08300.620 ppb
2015-04-229588-801-11353.40 ppb
2015-07-239588-800-08354.60 ppb
2015-07-239588-803-114010.00 ppb
2015-07-239588-802-08202.10 ppb
2015-07-239588-801-12055.40 ppb
2015-10-269588-801-11507.40 ppb
2015-10-269588-800-0830ND
2015-10-269588-803-11357.00 ppb
2015-10-269588-802-08201.20 ppb
2016-01-269588-801-12108.00 ppb
2016-01-269588-800-0850ND
2016-01-269588-803-11557.10 ppb
2016-01-269588-802-0840ND
2016-04-229588-801-12106.30 ppb
2016-04-229588-800-08401.10 ppb
2016-04-229588-803-11354.10 ppb
2016-04-229588-802-0820ND
2016-07-269588-803-1110ND
2016-07-269588-801-11252.80 ppb
2016-07-269588-800-0835ND
2016-07-269588-802-0825ND
2016-10-269588-803-11503.30 ppb
2016-10-269588-801-12055.00 ppb
2016-10-269588-802-0845ND
2016-10-269588-800-09002.80 ppb
2017-01-249588-802-0835ND
2017-01-249588-803-11502.30 ppb
2017-01-249588-801-12103.30 ppb
2017-01-249588-800-0850ND
2017-04-249588-802-13451.80 ppb
2017-04-249588-800-1355ND
2017-04-249588-801-13304.90 ppb
2017-04-249588-803-13154.20 ppb
2017-07-279588-800-14051.60 ppb
2017-07-279588-801-13301.60 ppb
2017-07-279588-803-13151.20 ppb
2017-07-279588-802-1345ND
2017-10-249588-803-11453.80 ppb
2017-10-249588-800-08402.40 ppb
2017-10-249588-802-0830ND
2017-10-249588-801-12104.60 ppb
2018-01-249588-803-11004.10 ppb
2018-01-249588-800-09001.40 ppb
2018-01-249588-801-11155.40 ppb
2018-01-249588-802-0850ND
2018-04-249588-801-12404.50 ppb
2018-04-249588-802-0830ND
2018-04-249588-803-11302.90 ppb
2018-04-249588-800-08402.40 ppb
2018-07-249588-801-11355.50 ppb
2018-07-249588-803-11152.90 ppb
2018-07-249588-802-08101.20 ppb
2018-07-249588-800-08204.20 ppb
2018-10-239588-801-11504.90 ppb
2018-10-239588-803-11252.40 ppb
2018-10-239588-802-0825ND
2018-10-239588-800-08350.550 ppb
2019-01-249588-800-09203.40 ppb
2019-01-249588-802-13154.80 ppb
2019-01-249588-801-13153.60 ppb
2019-01-249588-803-12453.00 ppb
2019-04-239588-800-08303.30 ppb
2019-04-239588-802-08203.50 ppb
2019-04-239588-803-11353.20 ppb
2019-04-239588-801-11505.60 ppb
2019-07-239588-803-10152.70 ppb
2019-07-239588-802-0755ND
2019-07-239588-800-08101.10 ppb
2019-07-239588-801-09305.20 ppb
2019-10-239588-803-11501.40 ppb
2019-10-239588-802-08202.80 ppb
2019-10-239588-800-08302.80 ppb
2019-10-239588-801-12055.60 ppb