Total trihalomethanes (TTHMs)
University of Connecticut - Main Campus
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 | 19.7 ppb | 24 | 24 | 6.80 ppb - 38.3 ppb |
| 2019 | 17.6 ppb | 24 | 24 | 9.50 ppb - 32.9 ppb |
| 2020 | 18.3 ppb | 23 | 23 | 1.80 ppb - 28.8 ppb |
| 2021 | 24.2 ppb | 16 | 16 | 9.50 ppb - 38.1 ppb |
| 2022 | 20.9 ppb | 16 | 16 | 14.9 ppb - 29.2 ppb |
| 2023 | 19.1 ppb | 16 | 16 | 11.2 ppb - 32.8 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 |
|---|---|---|
| 2018-03-15 | CA02987TTHM | 19.7 ppb |
| 2018-03-15 | CA02988TTHM | 10.4 ppb |
| 2018-03-15 | CA02989TTHM | 25.7 ppb |
| 2018-03-15 | CA02990TTHM | 12.5 ppb |
| 2018-06-12 | CA68568TTHM | 23.6 ppb |
| 2018-06-12 | CA68569TTHM | 20.4 ppb |
| 2018-06-12 | CA68570TTHM | 23.8 ppb |
| 2018-06-12 | CA68571TTHM | 11.4 ppb |
| 2018-09-19 | DBP 200506182 | 25.4 ppb |
| 2018-09-19 | DBP 200506184 | 38.3 ppb |
| 2018-09-19 | DBP 200506186 | 19.2 ppb |
| 2018-09-19 | DBP 200506189 | 13.7 ppb |
| 2018-09-25 | DBP 200506720 | 23.1 ppb |
| 2018-09-25 | DBP 200506721 | 38.1 ppb |
| 2018-09-25 | DBP 200506722 | 17.6 ppb |
| 2018-09-25 | DBP 200506723 | 19.7 ppb |
| 2018-09-26 | DBP 200506966 | 14.8 ppb |
| 2018-09-27 | DBP 200507073 | 21.5 ppb |
| 2018-12-04 | DBP 200514724 | 6.80 ppb |
| 2018-12-04 | DBP 200514725 | 28.3 ppb |
| 2018-12-04 | DBP 200514726 | 15.8 ppb |
| 2018-12-04 | DBP 200514728 | 13.4 ppb |
| 2018-12-17 | DBP 200516281 | 16.7 ppb |
| 2018-12-17 | DBP 200516282 | 13.3 ppb |
| 2019-03-18 | DBP 200525024 | 12.2 ppb |
| 2019-03-18 | DBP 200525026 | 11.9 ppb |
| 2019-03-18 | DBP 200525029 | 17.0 ppb |
| 2019-03-18 | DBP 200525031 | 18.7 ppb |
| 2019-03-18 | DBP 200525033 | 13.8 ppb |
| 2019-03-18 | DBP 200525034 | 11.0 ppb |
| 2019-06-24 | DBP 200537541 | 22.6 ppb |
| 2019-06-24 | DBP 200537542 | 17.7 ppb |
| 2019-06-24 | DBP 200537543 | 14.6 ppb |
| 2019-06-25 | DBP 200537806 | 14.1 ppb |
| 2019-06-25 | DBP 200537807 | 22.3 ppb |
| 2019-06-25 | DBP 200537808 | 32.4 ppb |
| 2019-09-16 | DBP 200549001 | 16.1 ppb |
| 2019-09-16 | DBP 200549002 | 9.50 ppb |
| 2019-09-16 | DBP 200549040 | 23.1 ppb |
| 2019-09-16 | DBP 200549041 | 32.2 ppb |
| 2019-09-16 | DBP 200549043 | 15.0 ppb |
| 2019-09-16 | DBP 200549044 | 15.5 ppb |
| 2019-12-09 | DBP 200559412 | 12.3 ppb |
| 2019-12-09 | DBP 200559416 | 10.1 ppb |
| 2019-12-09 | DBP 200559419 | 17.2 ppb |
| 2019-12-09 | DBP 200559422 | 32.9 ppb |
| 2019-12-09 | DBP 200559425 | 17.0 ppb |
| 2019-12-09 | DBP 200559427 | 13.2 ppb |
| 2020-03-10 | DBP 200568861 | 17.2 ppb |
| 2020-03-10 | DBP 200568862 | 14.6 ppb |
| 2020-03-10 | DBP 200568863 | 16.2 ppb |
| 2020-03-10 | DBP 200568864 | 19.9 ppb |
| 2020-03-10 | DBP 200568865 | 16.9 ppb |
| 2020-03-10 | DBP 200568866 | 14.1 ppb |
| 2020-04-28 | VOC1 200573885 | 1.80 ppb |
| 2020-06-08 | DBP 200578348 | 16.8 ppb |
| 2020-06-08 | DBP 200578349 | 21.8 ppb |
| 2020-06-08 | DBP 200578350 | 14.2 ppb |
| 2020-06-08 | DBP 200578351 | 27.1 ppb |
| 2020-06-08 | DBP 200578352 | 17.3 ppb |
| 2020-06-08 | DBP 200578353 | 14.4 ppb |
| 2020-09-08 | DBP 200589310 | 28.8 ppb |
| 2020-09-08 | DBP 200589311 | 28.5 ppb |
| 2020-09-08 | DBP 200589312 | 22.5 ppb |
| 2020-09-08 | DBP 200589313 | 14.5 ppb |
| 2020-09-08 | DBP 200589314 | 28.5 ppb |
| 2020-09-08 | DBP 200589315 | 13.9 ppb |
| 2020-12-14 | DBP 200601156 | 14.9 ppb |
| 2020-12-14 | DBP 200601157 | 21.6 ppb |
| 2020-12-14 | DBP 200601385 | 20.6 ppb |
| 2020-12-15 | DBP 200601475 | 14.0 ppb |
| 2021-03-10 | DBP 200609379 | 14.4 ppb |
| 2021-03-10 | DBP 200609380 | 18.3 ppb |
| 2021-03-10 | DBP 200609381 | 9.50 ppb |
| 2021-03-10 | DBP 200609382 | 18.0 ppb |
| 2021-06-01 | DBP 200619042 | 32.8 ppb |
| 2021-06-01 | DBP 200619044 | 26.0 ppb |
| 2021-06-01 | DBP 200619046 | 16.6 ppb |
| 2021-06-01 | DBP 200619048 | 33.3 ppb |
| 2021-09-08 | 300054204 300054209 | 29.6 ppb |
| 2021-09-08 | 300054205 300054211 | 29.2 ppb |
| 2021-09-08 | 300054206 300054213 | 12.8 ppb |
| 2021-09-08 | 300054207 300054215 | 38.1 ppb |
| 2021-12-07 | D300114234 300114239 | 27.7 ppb |
| 2021-12-07 | D300114235 300114241 | 19.7 ppb |
| 2021-12-07 | D300114236 300114243 | 25.0 ppb |
| 2021-12-07 | D300114237 300114245 | 35.6 ppb |
| 2022-03-07 | CK80432 | 20.4 ppb |
| 2022-03-07 | CK80433 | 18.2 ppb |
| 2022-03-07 | CK80434 | 19.5 ppb |
| 2022-03-07 | CK80435 | 28.1 ppb |
| 2022-06-02 | CL46810 | 19.0 ppb |
| 2022-06-02 | CL46811 | 18.8 ppb |
| 2022-06-02 | CL46812 | 21.4 ppb |
| 2022-06-02 | CL46813 | 24.3 ppb |
| 2022-09-12 | CM28524 | 21.3 ppb |
| 2022-09-12 | CM28525 | 24.9 ppb |
| 2022-09-12 | CM28526 | 29.2 ppb |
| 2022-09-12 | CM28527 | 21.1 ppb |
| 2022-12-12 | CN02522 | 18.2 ppb |
| 2022-12-12 | CN02523 | 16.5 ppb |
| 2022-12-12 | CN02524 | 14.9 ppb |
| 2022-12-12 | CN02525 | 18.6 ppb |
| 2023-03-08 | CN55281 | 16.0 ppb |
| 2023-03-08 | CN55282 | 17.5 ppb |
| 2023-03-08 | CN55283 | 12.5 ppb |
| 2023-03-08 | CN55284 | 18.8 ppb |
| 2023-06-05 | CO19179 | 29.3 ppb |
| 2023-06-05 | CO19180 | 19.3 ppb |
| 2023-06-05 | CO19181 | 11.2 ppb |
| 2023-06-05 | CO19182 | 20.9 ppb |
| 2023-09-11 | CO94210 | 22.2 ppb |
| 2023-09-11 | CO94211 | 21.8 ppb |
| 2023-09-11 | CO94212 | 14.4 ppb |
| 2023-09-11 | CO94213 | 32.8 ppb |
| 2023-12-05 | CP59865 | 16.4 ppb |
| 2023-12-05 | CP59866 | 18.3 ppb |
| 2023-12-05 | CP59867 | 14.7 ppb |
| 2023-12-05 | CP59868 | 19.2 ppb |