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EWG's Tap Water Database — 2021 UPDATE

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Total trihalomethanes (TTHMs)

Vernon Water Department

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.

 

60

Samples

0

Samples exceeding legal limit (MCL)

30

Samples exceeding
health guidelines

Testing results - average by year

 
YearAverage resultSamples takenDetectionsRange of results
20146.67 ppb126ND - 27.2 ppb
20154.41 ppb84ND - 26.5 ppb
2016N/A00N/A
201714.0 ppb85ND - 29.8 ppb
20188.69 ppb165ND - 48.5 ppb
201917.1 ppb1610ND - 31.1 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
2014-02-043761-803-12131.80 ppb
2014-02-043761-802-1118ND
2014-02-043761-801-11551.80 ppb
2014-02-043761-800-1139ND
2014-05-063761-803-1240ND
2014-05-063761-802-1215ND
2014-05-063761-801-12551.30 ppb
2014-05-063761-800-1310ND
2014-08-053761-803-120423.1 ppb
2014-08-053761-802-1059ND
2014-08-053761-801-114127.2 ppb
2014-08-053761-800-094724.8 ppb
2015-02-033761-802-1030ND
2015-02-033761-803-11333.00 ppb
2015-02-033761-801-1145ND
2015-02-033761-800-1122ND
2015-05-053761-803-10433.30 ppb
2015-05-053761-802-1104ND
2015-05-053761-800-120326.5 ppb
2015-05-053761-801-10192.50 ppb
2017-08-013761-800-1115ND
2017-08-013761-801-131529.8 ppb
2017-08-013761-803-113527.8 ppb
2017-08-013761-802-1050ND
2017-11-013761-803-11402.80 ppb
2017-11-013761-800-130525.9 ppb
2017-11-013761-801-104325.5 ppb
2017-11-013761-802-1117ND
2018-02-063761-802-1126ND
2018-02-063761-800-110348.5 ppb
2018-02-063761-801-101329.9 ppb
2018-02-063761-803-103336.5 ppb
2018-05-013761-802-1208ND
2018-05-013761-800-1001ND
2018-05-013761-801-131513.0 ppb
2018-05-013761-803-1300ND
2018-08-073761-802-1320ND
2018-08-073761-800-1141ND
2018-08-073761-801-104711.2 ppb
2018-08-073761-803-1103ND
2018-11-063761-803-1131ND
2018-11-063761-800-1028ND
2018-11-063761-802-1049ND
2018-11-063761-801-1109ND
2019-02-063761-801-100326.0 ppb
2019-02-063761-803-094228.2 ppb
2019-02-063761-802-1051ND
2019-02-063761-800-102321.7 ppb
2019-05-073761-803-105930.8 ppb
2019-05-073761-801-112028.2 ppb
2019-05-073761-802-1032ND
2019-05-073761-800-113926.6 ppb
2019-08-063761-800-110331.1 ppb
2019-08-063761-802-1130ND
2019-08-063761-801-100026.7 ppb
2019-08-063761-803-131626.6 ppb
2019-11-053761-800-140127.7 ppb
2019-11-053761-801-1320ND
2019-11-053761-803-1307ND
2019-11-053761-802-1341ND