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EWG's Tap Water Database — 2021 UPDATE

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Total trihalomethanes (TTHMs)

Golden State Water Company - Tanglewood

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

 

52

Samples

0

Samples exceeding legal limit (MCL)

5

Samples exceeding
health guidelines

Testing results - average by year

 
YearAverage resultSamples takenDetectionsRange of results
20140.973 ppb113ND - 5.80 ppb
2015ND90ND
2016ND80ND
2017ND80ND
2018ND80ND
20190.713 ppb82ND - 4.60 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
2014-01-082706-009-0915ND
2014-01-222706-008-08054.40 ppb
2014-01-222706-007-0755ND
2014-04-022706-009-1015ND
2014-04-022706-008-0740ND
2014-04-022706-007-07505.80 ppb
2014-07-012706-008-0930ND
2014-07-012706-007-0945ND
2014-07-302706-009-1030ND
2014-10-082706-008-0925ND
2014-10-105867-007-11200.500 ppb
2015-01-062706-007-1605ND
2015-01-062706-008-1550ND
2015-01-212706-009-0800ND
2015-04-012706-007-0815ND
2015-04-012706-008-0805ND
2015-07-222706-007-0815ND
2015-07-222706-008-0750ND
2015-10-072706-007-0840ND
2015-10-072706-008-0910ND
2016-01-192706-007-1420ND
2016-01-192706-008-1405ND
2016-04-272706-007-0815ND
2016-04-272706-008-0820ND
2016-07-062706-007-0810ND
2016-07-062706-008-0800ND
2016-10-052706-008-0815ND
2016-10-052706-007-0805ND
2017-01-179590-008-1115ND
2017-01-179590-007-1100ND
2017-04-049590-008-1155ND
2017-04-049590-007-1140ND
2017-07-119590-008-1020ND
2017-07-119590-007-1030ND
2017-10-109590-008-1145ND
2017-10-319590-007-1100ND
2018-01-099590-008-0915ND
2018-01-099590-007-0935ND
2018-04-179590-008-0825ND
2018-04-179590-007-0820ND
2018-07-179590-008-0905ND
2018-07-179590-007-0907ND
2018-10-099590-008-0945ND
2018-10-099590-007-0926ND
2019-01-089590-008-1300ND
2019-01-089590-007-1315ND
2019-04-029590-008-0835ND
2019-04-029590-007-09234.60 ppb
2019-07-029590-008-12401.10 ppb
2019-07-029590-007-1225ND
2019-10-019590-008-1205ND
2019-10-019590-007-1215ND