Know Your Environment. Protect Your Health.

Total trihalomethanes (TTHMs)

Rice University

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.

 

46

Samples

0

Samples exceeding legal limit (MCL)

23

Samples exceeding
health guidelines

Testing results - average by year

 
YearAverage resultSamples takenDetectionsRange of results
201815.0 ppb86ND - 39.4 ppb
201919.3 ppb87ND - 38.1 ppb
202017.5 ppb86ND - 36.0 ppb
20210.150 ppb81ND - 1.20 ppb
20226.48 ppb83ND - 25.4 ppb
2023ND60ND

ppb = parts per billion

State, National, and Health Guidelines for Drinking Water

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
2018-01-11AE089123.30 ppb
2018-03-13AE181296.50 ppb
2018-04-03AE2100620.5 ppb
2018-04-03AE2097413.1 ppb
2018-07-09AE3259139.4 ppb
2018-07-09AE3259537.1 ppb
2018-10-10AE43071ND
2018-10-10AE43072ND
2019-01-16AE501148.10 ppb
2019-01-16AE501177.30 ppb
2019-04-04AE6119417.4 ppb
2019-04-04AE61195ND
2019-07-09AE7364030.7 ppb
2019-07-09AE7366538.1 ppb
2019-11-15AE8951523.5 ppb
2019-11-15AE8951729.1 ppb
2020-02-07AE975924.60 ppb
2020-02-07AE97595ND
2020-04-27AF0823432.2 ppb
2020-04-27AF0823631.5 ppb
2020-07-23AF2043236.0 ppb
2020-07-23AF2043433.4 ppb
2020-10-22AF316472.60 ppb
2020-10-22AF31646ND
2021-02-08AF42911ND
2021-02-08AF42912ND
2021-04-13AF49943ND
2021-04-13AF499461.20 ppb
2021-08-25AF67912ND
2021-08-25AF67916ND
2021-10-25AF74461ND
2021-10-25AF74462ND
2022-02-02AF83245ND
2022-02-02AF83246ND
2022-05-02AF95056ND
2022-05-02AF950573.00 ppb
2022-09-09AG12372ND
2022-09-09AG12374ND
2022-10-12AG1681125.4 ppb
2022-10-12AG1682423.4 ppb
2023-02-02AG27106ND
2023-02-02AG27107ND
2023-04-21AG37646ND
2023-04-21AG37647ND
2023-08-16AG52811ND
2023-08-16AG52829ND