Total trihalomethanes (TTHMs)
Connecticut Water Company - Northern Region-Western System
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.
Samples
Samples exceeding legal limit (MCL)
Samples exceeding
health guidelines
Testing results - average by year
| Year | Average result | Samples taken | Detections | Range of results |
|---|---|---|---|---|
| 2013 | N/A | 0 | 0 | N/A |
| 2014 | 36.6 ppb | 32 | 32 | 14.5 ppb - 75.6 ppb |
| 2015 | 32.8 ppb | 32 | 32 | 12.9 ppb - 65.1 ppb |
| 2016 | 32.6 ppb | 32 | 32 | 12.3 ppb - 64.6 ppb |
| 2017 | 40.4 ppb | 32 | 32 | 12.2 ppb - 79.9 ppb |
| 2018 | 53.0 ppb | 35 | 35 | 21.8 ppb - 103.4 ppb |
| 2019 | 40.8 ppb | 32 | 32 | 16.3 ppb - 70.5 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 |
|---|---|---|
| 2014-02-04 | 1747THM | 39.9 ppb |
| 2014-02-04 | 1748THM | 18.0 ppb |
| 2014-02-04 | 1749THM | 38.9 ppb |
| 2014-02-04 | 1750THM | 18.9 ppb |
| 2014-02-04 | 1751THM | 23.3 ppb |
| 2014-02-04 | 1752THM | 20.5 ppb |
| 2014-02-04 | 1753THM | 38.0 ppb |
| 2014-02-04 | 1754THM | 52.0 ppb |
| 2014-05-06 | 6108THM | 47.9 ppb |
| 2014-05-06 | 6109THM | 75.6 ppb |
| 2014-05-06 | 6110THM | 29.7 ppb |
| 2014-05-06 | 6111THM | 72.7 ppb |
| 2014-05-06 | 6112THM | 20.0 ppb |
| 2014-05-06 | 6113THM | 59.2 ppb |
| 2014-05-06 | 6114THM | 23.8 ppb |
| 2014-05-09 | 6107THM | 36.5 ppb |
| 2014-08-05 | BG88648TTHM | 28.3 ppb |
| 2014-08-05 | BG88649TTHM | 49.5 ppb |
| 2014-08-05 | BG88650TTHM | 53.7 ppb |
| 2014-08-05 | BG88651TTHM | 31.2 ppb |
| 2014-08-05 | BG88652TTHM | 63.3 ppb |
| 2014-08-05 | BG88653TTHM | 14.5 ppb |
| 2014-08-05 | BG88654TTHM | 38.7 ppb |
| 2014-08-05 | BG88655TTHM | 30.3 ppb |
| 2014-11-25 | BH46470TTHM | 23.5 ppb |
| 2014-11-25 | BH46471TTHM | 43.6 ppb |
| 2014-11-25 | BH46472TTHM | 40.4 ppb |
| 2014-11-25 | BH46473TTHM | 36.8 ppb |
| 2014-11-25 | BH46474TTHM | 44.6 ppb |
| 2014-11-25 | BH46475TTHM | 16.8 ppb |
| 2014-11-25 | BH46476TTHM | 19.7 ppb |
| 2014-11-25 | BH46477TTHM | 19.8 ppb |
| 2015-02-25 | BH77224TTHM | 15.3 ppb |
| 2015-02-25 | BH77221TTHM | 41.3 ppb |
| 2015-02-25 | BH77226TTHM | 22.9 ppb |
| 2015-02-25 | BH77222TTHM | 27.9 ppb |
| 2015-02-25 | BH77220TTHM | 50.9 ppb |
| 2015-02-25 | BH77225TTHM | 27.8 ppb |
| 2015-02-25 | BH77219TTHM | 20.5 ppb |
| 2015-02-25 | BH77223TTHM | 53.7 ppb |
| 2015-05-21 | BJ20485TTHM | 33.3 ppb |
| 2015-05-21 | BJ20484TTHM | 31.0 ppb |
| 2015-05-21 | BJ20486TTHM | 14.3 ppb |
| 2015-05-21 | BJ20481TTHM | 19.2 ppb |
| 2015-05-21 | BJ20488TTHM | 15.2 ppb |
| 2015-05-21 | BJ20483TTHM | 18.2 ppb |
| 2015-05-21 | BJ20482TTHM | 19.4 ppb |
| 2015-05-21 | BJ20487TTHM | 12.9 ppb |
| 2015-08-20 | BJ78786TTHM | 17.0 ppb |
| 2015-08-20 | BJ78787TTHM | 28.7 ppb |
| 2015-08-20 | BJ78781TTHM | 30.3 ppb |
| 2015-08-20 | BJ78784TTHM | 55.0 ppb |
| 2015-08-20 | BJ78782TTHM | 65.1 ppb |
| 2015-08-20 | BJ78783TTHM | 49.2 ppb |
| 2015-08-20 | BJ78785TTHM | 64.8 ppb |
| 2015-08-20 | BJ78788TTHM | 29.4 ppb |
| 2015-11-24 | BK27969TTHM | 35.3 ppb |
| 2015-11-24 | BK27968TTHM | 55.6 ppb |
| 2015-11-24 | BK27967TTHM | 55.5 ppb |
| 2015-11-24 | BK27966TTHM | 27.9 ppb |
| 2015-11-24 | BK27970TTHM | 57.7 ppb |
| 2015-11-24 | BK27972TTHM | 17.2 ppb |
| 2015-11-24 | BK27971TTHM | 15.1 ppb |
| 2015-11-24 | BK27973TTHM | 20.5 ppb |
| 2016-02-04 | BK61857TTHM | 21.4 ppb |
| 2016-02-04 | BK61858TTHM | 43.2 ppb |
| 2016-02-04 | BK61859TTHM | 38.0 ppb |
| 2016-02-04 | BK61860TTHM | 35.3 ppb |
| 2016-02-04 | BK61861TTHM | 45.5 ppb |
| 2016-02-04 | BK61862TTHM | 14.8 ppb |
| 2016-02-04 | BK61863TTHM | 18.1 ppb |
| 2016-02-04 | BK61864TTHM | 19.5 ppb |
| 2016-05-05 | BN26300TTHM | 22.2 ppb |
| 2016-05-05 | BN26301TTHM | 56.2 ppb |
| 2016-05-05 | BN26302TTHM | 43.6 ppb |
| 2016-05-05 | BN26303TTHM | 40.7 ppb |
| 2016-05-05 | BN26304TTHM | 57.1 ppb |
| 2016-05-05 | BN26305TTHM | 12.3 ppb |
| 2016-05-05 | BN26306TTHM | 17.7 ppb |
| 2016-05-05 | BN26307TTHM | 20.7 ppb |
| 2016-08-18 | BN94948TTHM | 37.9 ppb |
| 2016-08-18 | BN94949TTHM | 64.6 ppb |
| 2016-08-18 | BN94950TTHM | 18.9 ppb |
| 2016-08-18 | BN94951TTHM | 36.1 ppb |
| 2016-08-18 | BN94952TTHM | 62.0 ppb |
| 2016-08-18 | BN94953TTHM | 14.0 ppb |
| 2016-08-18 | BN94954TTHM | 40.2 ppb |
| 2016-08-18 | BN94955TTHM | 27.9 ppb |
| 2016-11-03 | BV75338TTHM | 24.1 ppb |
| 2016-11-03 | BV75339TTHM | 58.0 ppb |
| 2016-11-03 | BV75340TTHM | 29.0 ppb |
| 2016-11-03 | BV75341TTHM | 20.0 ppb |
| 2016-11-03 | BV75342TTHM | 55.0 ppb |
| 2016-11-03 | BV75343TTHM | 16.7 ppb |
| 2016-11-03 | BV75344TTHM | 15.4 ppb |
| 2016-11-03 | BV75345TTHM | 18.0 ppb |
| 2017-02-02 | BX44867TTHM | 18.3 ppb |
| 2017-02-02 | BX44868TTHM | 48.0 ppb |
| 2017-02-02 | BX44869TTHM | 36.0 ppb |
| 2017-02-02 | BX44870TTHM | 25.0 ppb |
| 2017-02-02 | BX44871TTHM | 49.0 ppb |
| 2017-02-02 | BX44872TTHM | 12.2 ppb |
| 2017-02-02 | BX44873TTHM | 16.5 ppb |
| 2017-02-02 | BX44874TTHM | 18.4 ppb |
| 2017-05-04 | BY15439TTHM | 19.7 ppb |
| 2017-05-04 | BY15440TTHM | 60.0 ppb |
| 2017-05-04 | BY15441TTHM | 20.0 ppb |
| 2017-05-04 | BY15442TTHM | 32.2 ppb |
| 2017-05-04 | BY15443TTHM | 61.0 ppb |
| 2017-05-04 | BY15444TTHM | 14.2 ppb |
| 2017-05-04 | BY15445TTHM | 27.8 ppb |
| 2017-05-04 | BY15446TTHM | 27.9 ppb |
| 2017-08-07 | BY79801TTHM | 46.2 ppb |
| 2017-08-07 | BY79802TTHM | 53.4 ppb |
| 2017-08-07 | BY79803TTHM | 41.8 ppb |
| 2017-08-07 | BY79804TTHM | 39.1 ppb |
| 2017-08-07 | BY79805TTHM | 54.1 ppb |
| 2017-08-07 | BY79806TTHM | 41.4 ppb |
| 2017-08-07 | BY79807TTHM | 37.4 ppb |
| 2017-08-07 | BY79808TTHM | 33.1 ppb |
| 2017-11-06 | BZ33918TTHM | 52.6 ppb |
| 2017-11-16 | BZ43465TTHM | 55.5 ppb |
| 2017-11-16 | BZ43466TTHM | 79.9 ppb |
| 2017-11-16 | BZ43467TTHM | 76.5 ppb |
| 2017-11-16 | BZ43468TTHM | 70.2 ppb |
| 2017-11-16 | BZ43469TTHM | 41.6 ppb |
| 2017-11-16 | BZ43470TTHM | 45.7 ppb |
| 2017-11-16 | BZ43471TTHM | 37.3 ppb |
| 2018-02-01 | BZ83504TTHM | 41.3 ppb |
| 2018-02-01 | BZ83505TTHM | 56.7 ppb |
| 2018-02-01 | BZ83506TTHM | 52.5 ppb |
| 2018-02-01 | BZ83507TTHM | 63.8 ppb |
| 2018-02-01 | BZ83508TTHM | 25.8 ppb |
| 2018-02-01 | BZ83509TTHM | 28.8 ppb |
| 2018-02-01 | BZ83510TTHM | 26.1 ppb |
| 2018-02-21 | BZ93283TTHM | 33.0 ppb |
| 2018-05-03 | CA41161TTHM | 39.8 ppb |
| 2018-05-03 | CA41162TTHM | 65.6 ppb |
| 2018-05-03 | CA41163TTHM | 58.4 ppb |
| 2018-05-03 | CA41164TTHM | 72.0 ppb |
| 2018-05-03 | CA41165TTHM | 21.8 ppb |
| 2018-05-03 | CA41166TTHM | 27.7 ppb |
| 2018-05-03 | CA41167TTHM | 29.0 ppb |
| 2018-05-03 | D8E0468-01VOC | 67.0 ppb |
| 2018-05-15 | CA48118TTHM | 45.6 ppb |
| 2018-08-02 | CB04020 | 48.3 ppb |
| 2018-08-02 | CB04021 | 103.4 ppb |
| 2018-08-02 | CB04022 | 69.5 ppb |
| 2018-08-02 | CB04023 | 83.4 ppb |
| 2018-08-02 | CB04024 | 38.5 ppb |
| 2018-08-02 | CB04025 | 54.6 ppb |
| 2018-08-02 | CB04026 | 55.5 ppb |
| 2018-08-06 | CB05840 | 62.2 ppb |
| 2018-08-10 | DBP 200502031 | 84.0 ppb |
| 2018-08-10 | CB09154 | 90.0 ppb |
| 2018-11-01 | DBP 200511133 | 58.6 ppb |
| 2018-11-01 | DBP 200511134 | 74.3 ppb |
| 2018-11-01 | DBP 200511135 | 77.1 ppb |
| 2018-11-01 | DBP 200511136 | 83.9 ppb |
| 2018-11-01 | DBP 200511137 | 34.7 ppb |
| 2018-11-01 | DBP 200511138 | 22.1 ppb |
| 2018-11-01 | DBP 200511139 | 26.9 ppb |
| 2018-11-05 | DBP 200511389 | 34.5 ppb |
| 2019-02-07 | DBP 200521083 | 16.3 ppb |
| 2019-02-07 | DBP 200521084 | 43.6 ppb |
| 2019-02-07 | DBP 200521085 | 17.2 ppb |
| 2019-02-07 | DBP 200521086 | 39.5 ppb |
| 2019-02-07 | DBP 200521087 | 17.8 ppb |
| 2019-02-07 | DBP 200521088 | 47.2 ppb |
| 2019-02-07 | DBP 200521089 | 35.8 ppb |
| 2019-02-11 | DBP 200521256 | 22.9 ppb |
| 2019-05-09 | DBP 200531575 | 34.5 ppb |
| 2019-05-09 | DBP 200531576 | 60.1 ppb |
| 2019-05-09 | DBP 200531577 | 56.2 ppb |
| 2019-05-09 | DBP 200531582 | 64.7 ppb |
| 2019-05-09 | DBP 200531584 | 21.3 ppb |
| 2019-05-09 | DBP 200531586 | 19.3 ppb |
| 2019-05-09 | DBP 200531587 | 19.1 ppb |
| 2019-05-13 | DBP 200531837 | 30.0 ppb |
| 2019-08-01 | DBP 200542722 | 38.1 ppb |
| 2019-08-01 | DBP 200542723 | 51.6 ppb |
| 2019-08-01 | DBP 200542724 | 38.9 ppb |
| 2019-08-01 | DBP 200542725 | 69.1 ppb |
| 2019-08-01 | DBP 200542726 | 40.8 ppb |
| 2019-08-01 | DBP 200542727 | 28.3 ppb |
| 2019-08-01 | DBP 200542728 | 26.4 ppb |
| 2019-08-13 | DBP 200544758 | 50.5 ppb |
| 2019-11-07 | DBP 200555828 | 67.1 ppb |
| 2019-11-07 | DBP 200555830 | 70.5 ppb |
| 2019-11-07 | DBP 200555831 | 63.8 ppb |
| 2019-11-07 | DBP 200555832 | 70.1 ppb |
| 2019-11-07 | DBP 200555833 | 48.8 ppb |
| 2019-11-07 | DBP 200555834 | 32.2 ppb |
| 2019-11-07 | DBP 200555835 | 26.5 ppb |
| 2019-11-18 | DBP 200557004 | 36.1 ppb |