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 |
|---|---|---|---|---|
| 2018 | 53.0 ppb | 35 | 35 | 21.8 ppb - 103.4 ppb |
| 2019 | 40.8 ppb | 32 | 32 | 16.3 ppb - 70.5 ppb |
| 2020 | 40.2 ppb | 33 | 33 | 10.9 ppb - 79.1 ppb |
| 2021 | 43.6 ppb | 32 | 32 | 9.50 ppb - 82.3 ppb |
| 2022 | 46.0 ppb | 32 | 32 | 20.7 ppb - 72.4 ppb |
| 2023 | 43.6 ppb | 32 | 32 | 18.9 ppb - 79.5 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 |
|---|---|---|
| 2018-02-01 | 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 |
| 2020-01-06 | DBP 200561665 | 27.9 ppb |
| 2020-02-06 | DBP 200565357 | 54.9 ppb |
| 2020-02-06 | DBP 200565358 | 50.0 ppb |
| 2020-02-06 | DBP 200565359 | 41.9 ppb |
| 2020-02-06 | DBP 200565360 | 34.8 ppb |
| 2020-02-06 | DBP 200565361 | 21.5 ppb |
| 2020-02-06 | DBP 200565362 | 15.8 ppb |
| 2020-02-07 | DBP 200565640 | 63.4 ppb |
| 2020-02-07 | DBP 200565641 | 26.1 ppb |
| 2020-05-07 | DBP 200575171 | 58.4 ppb |
| 2020-05-07 | DBP 200575173 | 79.1 ppb |
| 2020-05-07 | DBP 200575175 | 25.3 ppb |
| 2020-05-07 | DBP 200575176 | 21.1 ppb |
| 2020-05-07 | DBP 200575177 | 35.9 ppb |
| 2020-05-08 | DBP 200575174 | 39.0 ppb |
| 2020-05-08 | DBP 200575172 | 44.3 ppb |
| 2020-05-08 | DBP 200575170 | 72.8 ppb |
| 2020-08-06 | DBP 200585744 | 39.0 ppb |
| 2020-08-06 | DBP 200585750 | 57.8 ppb |
| 2020-08-06 | DBP 200585753 | 49.9 ppb |
| 2020-08-06 | DBP 200585754 | 51.1 ppb |
| 2020-08-07 | DBP 200585755 | 66.8 ppb |
| 2020-08-07 | DBP 200585756 | 28.8 ppb |
| 2020-08-07 | DBP 200585757 | 31.1 ppb |
| 2020-08-07 | DBP 200585758 | 49.1 ppb |
| 2020-11-05 | DBP 200597356 | 19.1 ppb |
| 2020-11-05 | DBP 200597357 | 64.4 ppb |
| 2020-11-05 | DBP 200597358 | 32.4 ppb |
| 2020-11-05 | DBP 200597359 | 12.4 ppb |
| 2020-11-05 | DBP 200597360 | 10.9 ppb |
| 2020-11-05 | DBP 200597361 | 18.9 ppb |
| 2020-11-12 | DBP 200598206 | 45.3 ppb |
| 2020-11-12 | DBP 200598210 | 36.6 ppb |
| 2021-02-11 | DBP 200606895 | 13.7 ppb |
| 2021-02-11 | DBP 200606896 | 19.1 ppb |
| 2021-02-11 | DBP 200606907 | 9.50 ppb |
| 2021-02-12 | DBP 200606911 | 21.6 ppb |
| 2021-02-16 | DBP 200606912 | 49.0 ppb |
| 2021-02-17 | DBP 200607112 | 27.8 ppb |
| 2021-02-22 | DBP 200607459 | 13.0 ppb |
| 2021-02-23 | DBP 200607645 | 33.6 ppb |
| 2021-05-13 | DBP 200617239 | 40.7 ppb |
| 2021-05-14 | DBP 200617236 | 53.1 ppb |
| 2021-05-14 | DBP 200617237 | 26.5 ppb |
| 2021-05-14 | DBP 200617238 | 21.0 ppb |
| 2021-05-20 | DBP 200618316 | 68.9 ppb |
| 2021-05-20 | DBP 200618317 | 28.6 ppb |
| 2021-05-20 | DBP 200618319 | 56.5 ppb |
| 2021-05-20 | DBP 200618321 | 60.8 ppb |
| 2021-08-12 | DBP 200628756 | 58.0 ppb |
| 2021-08-12 | DBP 200628757 | 31.0 ppb |
| 2021-08-12 | DBP 200628758 | 76.5 ppb |
| 2021-08-12 | DBP 200628759 | 34.8 ppb |
| 2021-08-12 | DBP 200628760 | 41.8 ppb |
| 2021-08-12 | DBP 200628761 | 53.9 ppb |
| 2021-08-25 | DBP 200629815 | 71.7 ppb |
| 2021-08-25 | DBP 200629816 | 76.8 ppb |
| 2021-11-04 | D300098348 300098357 | 46.6 ppb |
| 2021-11-04 | D300098349 300098359 | 26.2 ppb |
| 2021-11-04 | D300098350 300098361 | 75.7 ppb |
| 2021-11-04 | D300098351 300098363 | 21.7 ppb |
| 2021-11-04 | D300098352 300098365 | 34.8 ppb |
| 2021-11-05 | D300098353 300098367 | 54.0 ppb |
| 2021-11-05 | D300098354 300098369 | 82.3 ppb |
| 2021-11-05 | D300098355 300098371 | 65.0 ppb |
| 2022-02-03 | CK29752 | 35.0 ppb |
| 2022-02-03 | CK29753 | 25.0 ppb |
| 2022-02-03 | CK29754 | 67.1 ppb |
| 2022-02-03 | CK29755 | 28.0 ppb |
| 2022-02-03 | CK29756 | 40.0 ppb |
| 2022-02-03 | CK29757 | 41.1 ppb |
| 2022-02-03 | CK29758 | 54.6 ppb |
| 2022-02-04 | CK31489 | 72.4 ppb |
| 2022-05-12 | CL31513 | 36.9 ppb |
| 2022-05-12 | CL31514 | 66.1 ppb |
| 2022-05-12 | CL31515 | 28.0 ppb |
| 2022-05-12 | CL31516 | 44.1 ppb |
| 2022-05-12 | CL31517 | 28.2 ppb |
| 2022-05-13 | CL31518 | 50.8 ppb |
| 2022-05-13 | CL31519 | 48.8 ppb |
| 2022-05-13 | CL31520 | 49.7 ppb |
| 2022-08-04 | CL98963 | 64.3 ppb |
| 2022-08-04 | CL98964 | 54.5 ppb |
| 2022-08-04 | CL98965 | 66.5 ppb |
| 2022-08-05 | CL98966 | 62.7 ppb |
| 2022-08-05 | CL98967 | 59.5 ppb |
| 2022-08-05 | CL98968 | 61.5 ppb |
| 2022-08-05 | CL98969 | 67.6 ppb |
| 2022-08-05 | CL98970 | 47.2 ppb |
| 2022-11-17 | CM90283 | 40.5 ppb |
| 2022-11-17 | CM90284 | 20.7 ppb |
| 2022-11-17 | CM90285 | 49.1 ppb |
| 2022-11-17 | CM90286 | 25.2 ppb |
| 2022-11-17 | CM90287 | 39.2 ppb |
| 2022-11-17 | CM90288 | 31.3 ppb |
| 2022-11-17 | CM90289 | 28.6 ppb |
| 2022-11-18 | CM90290 | 37.7 ppb |
| 2023-02-02 | CN37077 | 18.9 ppb |
| 2023-02-02 | CN37078 | 27.4 ppb |
| 2023-02-02 | CN37079 | 39.5 ppb |
| 2023-02-02 | CN37080 | 19.0 ppb |
| 2023-02-02 | CN37081 | 28.8 ppb |
| 2023-02-02 | CN37082 | 28.9 ppb |
| 2023-02-02 | CN37083 | 37.3 ppb |
| 2023-02-02 | CN37084 | 34.1 ppb |
| 2023-05-12 | CO06294 | 30.9 ppb |
| 2023-05-12 | CO06295 | 72.6 ppb |
| 2023-05-12 | CO06296 | 33.6 ppb |
| 2023-05-12 | CO06297 | 50.7 ppb |
| 2023-05-12 | CO06298 | 57.0 ppb |
| 2023-05-12 | CO06299 | 59.3 ppb |
| 2023-05-18 | CO09386 | 51.7 ppb |
| 2023-05-18 | CO09387 | 61.8 ppb |
| 2023-08-10 | CO73376 | 39.5 ppb |
| 2023-08-10 | CO73377 | 70.9 ppb |
| 2023-08-10 | CO73378 | 76.7 ppb |
| 2023-08-11 | CO73379 | 39.0 ppb |
| 2023-08-11 | CO73380 | 50.1 ppb |
| 2023-08-11 | CO73381 | 56.2 ppb |
| 2023-08-11 | CO73382 | 57.3 ppb |
| 2023-08-11 | CO73383 | 79.5 ppb |
| 2023-11-16 | CP50449 | 41.5 ppb |
| 2023-11-16 | CP50450 | 32.2 ppb |
| 2023-11-16 | CP50451 | 48.9 ppb |
| 2023-11-16 | CP50452 | 26.6 ppb |
| 2023-11-16 | CP50453 | 23.2 ppb |
| 2023-11-16 | CP50454 | 45.7 ppb |
| 2023-11-16 | CP50455 | 20.9 ppb |
| 2023-11-17 | CP50456 | 34.2 ppb |