Know Your Environment. Protect Your Health.

Total trihalomethanes (TTHMs)

Watertown Water & Sewer Authority

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.

 

96

Samples

16

Samples exceeding legal limit (MCL)

96

Samples exceeding
health guidelines

Testing results - average by year

 
YearAverage resultSamples takenDetectionsRange of results
201864.6 ppb161630.5 ppb - 99.8 ppb
201961.2 ppb161629.6 ppb - 91.8 ppb
202061.1 ppb161630.8 ppb - 109.0 ppb
202163.4 ppb161627.6 ppb - 99.0 ppb
202253.7 ppb161638.8 ppb - 79.9 ppb
202351.4 ppb161627.3 ppb - 92.2 ppb

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
2018-03-07DBP 20048953448.0 ppb
2018-03-07DBP 20048953553.5 ppb
2018-03-07DBP 20048953654.7 ppb
2018-03-07DBP 20048953363.3 ppb
2018-06-06DBP 20049632879.1 ppb
2018-06-06DBP 20049632972.8 ppb
2018-06-06DBP 20049633068.7 ppb
2018-06-06DBP 20049633173.2 ppb
2018-09-05DBP 20050406187.8 ppb
2018-09-05DBP 20050406299.8 ppb
2018-09-05DBP 20050406385.4 ppb
2018-09-05DBP 20050406469.3 ppb
2018-12-05DBP 20051498051.2 ppb
2018-12-05DBP 20051498249.4 ppb
2018-12-05DBP 20051498146.4 ppb
2018-12-05DBP 20051497830.5 ppb
2019-03-06DBP 20052370857.6 ppb
2019-03-06DBP 20052370942.2 ppb
2019-03-06DBP 20052371045.4 ppb
2019-03-06DBP 20052371134.7 ppb
2019-06-05DBP 20053506867.1 ppb
2019-06-05DBP 20053506979.2 ppb
2019-06-05DBP 20053507060.2 ppb
2019-06-05DBP 20053507167.7 ppb
2019-09-05DBP 20054763791.6 ppb
2019-09-05DBP 20054764078.0 ppb
2019-09-05DBP 20054763986.8 ppb
2019-09-05DBP 20054763691.8 ppb
2019-12-05DBP 20055914729.6 ppb
2019-12-05DBP 20055914848.1 ppb
2019-12-05DBP 20055914937.8 ppb
2019-12-05DBP 20055914662.0 ppb
2020-03-04DBP 20056819757.3 ppb
2020-03-04DBP 20056819830.8 ppb
2020-03-04DBP 20056819940.9 ppb
2020-03-04DBP 20056820031.3 ppb
2020-06-03DBP 20057785556.2 ppb
2020-06-03DBP 20057785658.0 ppb
2020-06-03DBP 20057785452.8 ppb
2020-06-03DBP 20057785373.6 ppb
2020-09-02DBP 200588679109.0 ppb
2020-09-02DBP 20058868088.7 ppb
2020-09-02DBP 20058868176.3 ppb
2020-09-02DBP 20058868285.7 ppb
2020-12-02DBP 20059979164.8 ppb
2020-12-02DBP 20059979242.3 ppb
2020-12-02DBP 20059979355.3 ppb
2020-12-02DBP 20059979453.9 ppb
2021-03-10DBP 20060934943.2 ppb
2021-03-10DBP 20060934655.6 ppb
2021-03-10DBP 20060934727.6 ppb
2021-03-10DBP 20060934840.7 ppb
2021-06-02DBP 20061913755.7 ppb
2021-06-02DBP 20061913960.8 ppb
2021-06-02DBP 20061914071.0 ppb
2021-06-02DBP 20061913683.0 ppb
2021-09-08300053894 30005389678.5 ppb
2021-09-08300053900 30005390283.7 ppb
2021-09-08300053903 30005390572.2 ppb
2021-09-22300065698 30006570099.0 ppb
2021-12-01D300110687 30011068960.5 ppb
2021-12-01D300110684 30011068662.3 ppb
2021-12-01D300110681 30011068351.2 ppb
2021-12-01D300110678 30011068069.8 ppb
2022-03-02D300151783 30015178546.4 ppb
2022-03-02D300151786 30015178844.1 ppb
2022-03-02D300151789 30015179138.8 ppb
2022-03-02D300151792 30015179444.6 ppb
2022-06-01D300192098 30019210063.4 ppb
2022-06-01D300192101 30019210355.1 ppb
2022-06-01D300192104 30019210655.2 ppb
2022-06-01D300192107 30019210958.1 ppb
2022-09-14D300244033 30024403574.8 ppb
2022-09-14D300244027 30024402955.8 ppb
2022-09-14D300244024 30024402679.9 ppb
2022-09-14D300244030 30024403271.1 ppb
2022-12-07D300282718 30028272044.7 ppb
2022-12-07D300282721 30028272339.0 ppb
2022-12-07D300282724 30028272643.9 ppb
2022-12-07D300282727 30028272943.9 ppb
2023-03-16D300321892 30032189444.1 ppb
2023-03-16D300321895 30032189727.3 ppb
2023-03-16D300321898 30032190040.8 ppb
2023-03-16D300321901 30032190331.3 ppb
2023-06-14D300365450 30036545236.4 ppb
2023-06-14D300365456 30036545848.3 ppb
2023-06-14D300365453 30036545549.9 ppb
2023-06-14D300365447 30036544956.0 ppb
2023-09-06D300410877 30041087988.9 ppb
2023-09-06D300410880 30041088282.3 ppb
2023-09-06D300410883 30041088585.5 ppb
2023-09-06D300410886 30041088892.2 ppb
2023-12-07D300456855 30045685735.7 ppb
2023-12-07D300456858 30045686029.1 ppb
2023-12-07D300456861 30045686337.7 ppb
2023-12-07D300456864 30045686636.4 ppb