Total trihalomethanes (TTHMs)
CTWC - Naugatuck Region-Central 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 | 39.3 ppb | 16 | 16 | 20.6 ppb - 51.5 ppb |
| 2019 | 35.5 ppb | 16 | 16 | 12.7 ppb - 48.7 ppb |
| 2020 | 30.6 ppb | 16 | 16 | 9.20 ppb - 60.9 ppb |
| 2021 | 29.0 ppb | 16 | 16 | 7.00 ppb - 46.3 ppb |
| 2022 | 31.6 ppb | 16 | 16 | 13.4 ppb - 55.5 ppb |
| 2023 | 27.6 ppb | 16 | 16 | 12.0 ppb - 48.5 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 |
|---|---|---|
| 2018-02-14 | BZ89698TTHM | 46.1 ppb |
| 2018-02-14 | BZ89699TTHM | 44.6 ppb |
| 2018-02-14 | BZ89700TTHM | 51.5 ppb |
| 2018-02-14 | BZ89697TTHM | 31.4 ppb |
| 2018-05-21 | CA50437TTHM | 34.8 ppb |
| 2018-05-21 | CA50438TTHM | 20.6 ppb |
| 2018-05-21 | CA50439TTHM | 38.0 ppb |
| 2018-05-21 | CA50440TTHM | 36.6 ppb |
| 2018-08-20 | CB14939 | 28.5 ppb |
| 2018-08-20 | CB14940 | 42.4 ppb |
| 2018-08-20 | CB14941 | 41.5 ppb |
| 2018-08-20 | CB14942 | 42.3 ppb |
| 2018-11-20 | DBP 200513504 | 46.8 ppb |
| 2018-11-20 | DBP 200513534 | 49.4 ppb |
| 2018-11-20 | DBP 200513506 | 29.2 ppb |
| 2018-11-20 | DBP 200513502 | 45.9 ppb |
| 2019-02-20 | DBP 200522447 | 38.4 ppb |
| 2019-02-20 | DBP 200522448 | 34.4 ppb |
| 2019-02-20 | DBP 200522449 | 38.8 ppb |
| 2019-02-20 | DBP 200522450 | 24.1 ppb |
| 2019-05-21 | DBP 200533257 | 35.2 ppb |
| 2019-05-21 | DBP 200533258 | 28.7 ppb |
| 2019-05-21 | DBP 200533259 | 36.5 ppb |
| 2019-05-21 | DBP 200533260 | 12.7 ppb |
| 2019-08-20 | DBP 200545891 | 43.9 ppb |
| 2019-08-20 | DBP 200545893 | 23.1 ppb |
| 2019-08-20 | DBP 200545892 | 40.7 ppb |
| 2019-08-20 | DBP 200545890 | 45.9 ppb |
| 2019-11-19 | DBP 200557405 | 48.0 ppb |
| 2019-11-19 | DBP 200557406 | 47.4 ppb |
| 2019-11-19 | DBP 200557407 | 21.9 ppb |
| 2019-11-19 | DBP 200557404 | 48.7 ppb |
| 2020-02-19 | DBP 200566880 | 32.5 ppb |
| 2020-02-19 | DBP 200566881 | 29.0 ppb |
| 2020-02-19 | DBP 200566882 | 36.9 ppb |
| 2020-02-19 | DBP 200566883 | 13.8 ppb |
| 2020-05-05 | DBP 200574629 | 16.2 ppb |
| 2020-05-05 | DBP 200574630 | 40.2 ppb |
| 2020-05-05 | DBP 200574628 | 25.5 ppb |
| 2020-05-05 | DBP 200574627 | 22.6 ppb |
| 2020-08-14 | DBP 200586717 | 60.9 ppb |
| 2020-08-14 | DBP 200586721 | 44.9 ppb |
| 2020-08-14 | DBP 200586722 | 27.6 ppb |
| 2020-08-14 | DBP 200586723 | 54.7 ppb |
| 2020-11-17 | DBP 200598529 | 21.7 ppb |
| 2020-11-17 | DBP 200598530 | 20.3 ppb |
| 2020-11-17 | DBP 200598531 | 9.20 ppb |
| 2020-11-17 | DBP 200598532 | 33.7 ppb |
| 2021-02-17 | DBP 200607091 | 22.7 ppb |
| 2021-02-17 | DBP 200607088 | 13.8 ppb |
| 2021-02-17 | DBP 200607089 | 13.0 ppb |
| 2021-02-17 | DBP 200607090 | 7.00 ppb |
| 2021-05-21 | DBP 200618174 | 26.7 ppb |
| 2021-05-21 | DBP 200618175 | 18.1 ppb |
| 2021-05-21 | DBP 200618176 | 41.2 ppb |
| 2021-05-21 | DBP 200618173 | 35.7 ppb |
| 2021-08-12 | DBP 200628919 | 38.1 ppb |
| 2021-08-12 | DBP 200628920 | 36.6 ppb |
| 2021-08-12 | DBP 200628921 | 20.8 ppb |
| 2021-08-12 | DBP 200628922 | 46.3 ppb |
| 2021-11-02 | D300094268 300094276 | 43.0 ppb |
| 2021-11-02 | D300094267 300094274 | 21.7 ppb |
| 2021-11-02 | D300094266 300094272 | 39.4 ppb |
| 2021-11-02 | D300094265 300094270 | 40.2 ppb |
| 2022-02-22 | CK73058 | 30.5 ppb |
| 2022-02-22 | CK73059 | 25.2 ppb |
| 2022-02-22 | CK73060 | 37.6 ppb |
| 2022-02-22 | CK73061 | 19.9 ppb |
| 2022-05-20 | CL36073 | 26.8 ppb |
| 2022-05-20 | CL36074 | 26.7 ppb |
| 2022-05-20 | CL36075 | 38.3 ppb |
| 2022-05-20 | CL36076 | 20.1 ppb |
| 2022-08-03 | CL96383 | 32.9 ppb |
| 2022-08-03 | CL96381 | 48.4 ppb |
| 2022-08-03 | CL96380 | 55.5 ppb |
| 2022-08-03 | CL96382 | 54.6 ppb |
| 2022-11-04 | CM79285 | 27.9 ppb |
| 2022-11-04 | CM79286 | 19.8 ppb |
| 2022-11-04 | CM79287 | 27.4 ppb |
| 2022-11-04 | CM79288 | 13.4 ppb |
| 2023-02-09 | CN41441 | 18.2 ppb |
| 2023-02-09 | CN41442 | 14.8 ppb |
| 2023-02-09 | CN41443 | 23.5 ppb |
| 2023-02-09 | CN41444 | 12.0 ppb |
| 2023-05-08 | CO01645 | 21.6 ppb |
| 2023-05-08 | CO01647 | 14.6 ppb |
| 2023-05-08 | CO01646 | 29.6 ppb |
| 2023-05-08 | CO01644 | 24.8 ppb |
| 2023-08-04 | CO68170 | 48.5 ppb |
| 2023-08-04 | CO68171 | 36.4 ppb |
| 2023-08-04 | CO68172 | 40.9 ppb |
| 2023-08-04 | CO68173 | 23.7 ppb |
| 2023-11-03 | CP41463 | 39.3 ppb |
| 2023-11-03 | CP41464 | 30.9 ppb |
| 2023-11-03 | CP41465 | 38.5 ppb |
| 2023-11-03 | CP41466 | 24.3 ppb |