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EWG's Tap Water Database — 2021 UPDATE

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Total trihalomethanes (TTHMs)

California Domestic Water Company

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

 

126

Samples

0

Samples exceeding legal limit (MCL)

47

Samples exceeding
health guidelines

Testing results - average by year

 
YearAverage resultSamples takenDetectionsRange of results
20140.390 ppb339ND - 2.90 ppb
20150.855 ppb338ND - 14.0 ppb
20163.81 ppb149ND - 25.0 ppb
20170.596 ppb166ND - 3.00 ppb
20180.608 ppb147ND - 1.80 ppb
20190.538 ppb168ND - 2.40 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
2014-01-299588-800-1405ND
2014-01-299588-801-14301.10 ppb
2014-01-299588-802-1415ND
2014-03-219588-014-0910ND
2014-04-073761-004-0854ND
2014-04-073761-005-0939ND
2014-04-073761-006-0903ND
2014-04-073761-007-0921ND
2014-04-073761-008-0815ND
2014-04-073761-009-0735ND
2014-04-073761-014-1025ND
2014-04-099588-004-1120ND
2014-04-099588-005-1115ND
2014-04-099588-006-1140ND
2014-04-099588-007-1130ND
2014-04-099588-008-1150ND
2014-04-093761-020-07211.40 ppb
2014-04-289588-800-13151.10 ppb
2014-04-289588-801-13401.40 ppb
2014-04-289588-802-1325ND
2014-07-299588-800-07301.20 ppb
2014-07-299588-801-07551.90 ppb
2014-07-299588-802-07401.10 ppb
2014-10-063761-004-0855ND
2014-10-063761-005-1024ND
2014-10-063761-006-0943ND
2014-10-063761-007-1000ND
2014-10-063761-008-0837ND
2014-10-063761-009-0750ND
2014-10-299588-800-12452.90 ppb
2014-10-299588-801-13150.780 ppb
2014-10-299588-802-1255ND
2014-12-153761-014-0945ND
2015-01-079588-014-0905ND
2015-01-279588-800-11303.60 ppb
2015-01-279588-801-11552.30 ppb
2015-01-279588-802-1140ND
2015-04-063761-004-0850ND
2015-04-063761-005-0555ND
2015-04-063761-006-0743ND
2015-04-063761-007-0757ND
2015-04-063761-008-0730ND
2015-04-063761-009-0525ND
2015-04-063761-014-0700ND
2015-04-149588-004-0855ND
2015-04-149588-006-0945ND
2015-04-149588-007-0955ND
2015-04-149588-008-0935ND
2015-04-159588-005-0915ND
2015-04-279588-800-11050.650 ppb
2015-04-279588-801-11300.570 ppb
2015-04-279588-802-1115ND
2015-07-309588-800-12104.80 ppb
2015-07-309588-801-12401.10 ppb
2015-07-309588-802-1225ND
2015-10-053761-004-0809ND
2015-10-053761-005-0943ND
2015-10-053761-006-0840ND
2015-10-053761-007-0921ND
2015-10-053761-008-0902ND
2015-10-053761-009-0725ND
2015-10-053761-014-1029ND
2015-10-279588-800-111014.0 ppb
2015-10-279588-801-11401.20 ppb
2015-10-279588-802-1125ND
2015-11-199588-020-1055ND
2016-01-279588-800-111525.0 ppb
2016-01-279588-801-11400.680 ppb
2016-01-279588-802-1130ND
2016-04-043761-009-0745ND
2016-04-269588-800-115510.00 ppb
2016-04-269588-801-1230ND
2016-04-269588-802-1210ND
2016-07-279588-800-11552.00 ppb
2016-07-279588-801-12251.30 ppb
2016-07-279588-802-12051.60 ppb
2016-10-033761-009-0729ND
2016-10-279588-800-11403.40 ppb
2016-10-279588-801-12153.60 ppb
2016-10-279588-802-12005.80 ppb
2017-01-269588-800-11153.00 ppb
2017-01-269588-801-11452.40 ppb
2017-01-269588-802-1130ND
2017-04-033761-009-0748ND
2017-04-193761-009-0935ND
2017-04-269588-800-11051.30 ppb
2017-04-269588-801-1135ND
2017-04-269588-802-1115ND
2017-07-269588-800-0710ND
2017-07-269588-801-07250.520 ppb
2017-07-269588-802-0700ND
2017-09-263761-009-0930ND
2017-10-023761-009-0729ND
2017-10-269588-800-11151.80 ppb
2017-10-269588-801-11450.520 ppb
2017-10-269588-802-1130ND
2018-01-299588-800-11301.50 ppb
2018-01-299588-801-1155ND
2018-01-299588-802-1140ND
2018-04-023761-009-0757ND
2018-04-269588-800-11201.80 ppb
2018-04-269588-801-11401.40 ppb
2018-04-269588-802-1130ND
2018-07-269588-800-10301.10 ppb
2018-07-269588-801-11001.40 ppb
2018-07-269588-802-1045ND
2018-10-013761-009-0740ND
2018-10-259588-800-12000.550 ppb
2018-10-259588-801-12300.760 ppb
2018-10-259588-802-1215ND
2019-01-289588-800-10400.690 ppb
2019-01-289588-801-11152.40 ppb
2019-01-289588-802-1055ND
2019-04-013761-009-0814ND
2019-04-269588-800-11201.10 ppb
2019-04-269588-801-11501.40 ppb
2019-04-269588-802-11350.530 ppb
2019-07-259588-800-0815ND
2019-07-259588-801-08300.580 ppb
2019-07-259588-802-0805ND
2019-10-073761-009-0800ND
2019-10-319588-803-0850ND
2019-10-319588-804-0910ND
2019-10-319588-805-09300.500 ppb
2019-10-319588-806-09451.40 ppb
2019-10-319588-807-1000ND