Total trihalomethanes (TTHMs)
Danbury Water Department
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 | 43.6 ppb | 32 | 32 | 14.5 ppb - 91.7 ppb |
| 2019 | 32.9 ppb | 34 | 34 | 13.7 ppb - 55.7 ppb |
| 2020 | 37.5 ppb | 32 | 32 | 15.1 ppb - 69.7 ppb |
| 2021 | 31.6 ppb | 41 | 41 | 8.36 ppb - 58.1 ppb |
| 2022 | 33.1 ppb | 32 | 32 | 4.40 ppb - 58.4 ppb |
| 2023 | 38.9 ppb | 36 | 36 | 13.2 ppb - 71.8 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 |
|---|---|---|
| 2018-03-14 | 211584GE | 39.8 ppb |
| 2018-03-14 | 211586GE | 33.7 ppb |
| 2018-03-14 | 211588GE | 39.3 ppb |
| 2018-03-14 | 211590GE | 38.8 ppb |
| 2018-03-14 | 211598GE | 38.5 ppb |
| 2018-03-15 | 211592GE | 32.2 ppb |
| 2018-03-15 | 211594GE | 37.1 ppb |
| 2018-03-15 | 211596GE | 39.4 ppb |
| 2018-06-19 | 215736GE | 42.7 ppb |
| 2018-06-19 | 215738GE | 36.9 ppb |
| 2018-06-19 | 215742GE | 45.5 ppb |
| 2018-06-19 | 215744GE | 46.2 ppb |
| 2018-06-19 | 215750GE | 41.8 ppb |
| 2018-06-20 | 215746GE | 47.8 ppb |
| 2018-06-20 | 215748GE | 53.0 ppb |
| 2018-06-20 | 215740GE | 40.4 ppb |
| 2018-09-14 | DBP 200505484 | 35.3 ppb |
| 2018-09-14 | DBP 200505486 | 42.7 ppb |
| 2018-09-14 | DBP 200505491 | 74.0 ppb |
| 2018-09-14 | DBP 200505493 | 63.5 ppb |
| 2018-09-14 | DBP 200505495 | 91.7 ppb |
| 2018-09-14 | DBP 200505497 | 46.1 ppb |
| 2018-09-14 | DBP 200505499 | 69.6 ppb |
| 2018-09-17 | DBP 200505658 | 81.3 ppb |
| 2018-12-14 | DBP 200516093 | 37.9 ppb |
| 2018-12-14 | DBP 200516094 | 14.5 ppb |
| 2018-12-14 | DBP 200516095 | 19.7 ppb |
| 2018-12-14 | DBP 200516096 | 33.5 ppb |
| 2018-12-14 | DBP 200516097 | 40.9 ppb |
| 2018-12-14 | DBP 200516098 | 16.7 ppb |
| 2018-12-14 | DBP 200516099 | 46.7 ppb |
| 2018-12-14 | DBP 200516100 | 27.8 ppb |
| 2019-03-14 | DBP 200524760 | 37.1 ppb |
| 2019-03-14 | DBP 200524761 | 15.9 ppb |
| 2019-03-14 | DBP 200524762 | 22.5 ppb |
| 2019-03-14 | DBP 200524763 | 40.7 ppb |
| 2019-03-14 | DBP 200524764 | 19.8 ppb |
| 2019-03-14 | DBP 200524765 | 25.7 ppb |
| 2019-03-14 | DBP 200524766 | 30.7 ppb |
| 2019-03-14 | DBP 200524767 | 18.8 ppb |
| 2019-06-20 | DBP 200537265 | 45.8 ppb |
| 2019-06-20 | DBP 200537266 | 21.8 ppb |
| 2019-06-20 | DBP 200537267 | 20.2 ppb |
| 2019-06-20 | DBP 200537268 | 51.5 ppb |
| 2019-06-20 | DBP 200537269 | 44.0 ppb |
| 2019-06-20 | DBP 200537270 | 41.8 ppb |
| 2019-06-20 | DBP 200537271 | 55.7 ppb |
| 2019-06-20 | DBP 200537272 | 29.9 ppb |
| 2019-08-15 | VOC1 200545121 | 31.5 ppb |
| 2019-08-15 | VOC1 200545122 | 31.4 ppb |
| 2019-09-19 | DBP 200549612 | 44.9 ppb |
| 2019-09-19 | DBP 200549613 | 21.9 ppb |
| 2019-09-19 | DBP 200549614 | 25.3 ppb |
| 2019-09-19 | DBP 200549615 | 47.5 ppb |
| 2019-09-19 | DBP 200549616 | 47.6 ppb |
| 2019-09-19 | DBP 200549617 | 48.8 ppb |
| 2019-09-19 | DBP 200549618 | 52.9 ppb |
| 2019-09-19 | DBP 200549619 | 36.5 ppb |
| 2019-12-19 | DBP 200560926 | 34.1 ppb |
| 2019-12-19 | DBP 200560927 | 14.4 ppb |
| 2019-12-19 | DBP 200560929 | 13.7 ppb |
| 2019-12-19 | DBP 200560930 | 24.7 ppb |
| 2019-12-19 | DBP 200560931 | 36.0 ppb |
| 2019-12-19 | DBP 200560932 | 33.9 ppb |
| 2019-12-19 | DBP 200560934 | 19.3 ppb |
| 2019-12-19 | DBP 200560935 | 32.7 ppb |
| 2020-03-19 | DBP 200569976 | 35.4 ppb |
| 2020-03-19 | DBP 200569977 | 20.0 ppb |
| 2020-03-19 | DBP 200569978 | 25.1 ppb |
| 2020-03-19 | DBP 200569979 | 53.4 ppb |
| 2020-03-19 | DBP 200569980 | 38.7 ppb |
| 2020-03-19 | DBP 200569981 | 19.8 ppb |
| 2020-03-19 | DBP 200569982 | 44.5 ppb |
| 2020-03-19 | DBP 200569983 | 24.9 ppb |
| 2020-06-18 | DBP 200579794 | 46.5 ppb |
| 2020-06-18 | DBP 200579795 | 25.1 ppb |
| 2020-06-18 | DBP 200579796 | 20.7 ppb |
| 2020-06-18 | DBP 200579797 | 51.3 ppb |
| 2020-06-18 | DBP 200579798 | 47.3 ppb |
| 2020-06-18 | DBP 200579799 | 22.9 ppb |
| 2020-06-18 | DBP 200579800 | 51.4 ppb |
| 2020-06-18 | DBP 200579801 | 27.8 ppb |
| 2020-09-17 | DBP 200590661 | 56.5 ppb |
| 2020-09-17 | DBP 200590662 | 34.8 ppb |
| 2020-09-17 | DBP 200590663 | 54.0 ppb |
| 2020-09-17 | DBP 200590664 | 69.7 ppb |
| 2020-09-17 | DBP 200590665 | 28.7 ppb |
| 2020-09-17 | DBP 200590666 | 24.1 ppb |
| 2020-09-17 | DBP 200590667 | 59.0 ppb |
| 2020-09-17 | DBP 200590668 | 53.3 ppb |
| 2020-12-18 | DBP 200601598 | 42.5 ppb |
| 2020-12-18 | DBP 200601599 | 15.9 ppb |
| 2020-12-18 | DBP 200601600 | 15.1 ppb |
| 2020-12-18 | DBP 200601601 | 27.6 ppb |
| 2020-12-18 | DBP 200601602 | 37.9 ppb |
| 2020-12-18 | DBP 200601603 | 43.9 ppb |
| 2020-12-18 | DBP 200601604 | 45.3 ppb |
| 2020-12-18 | DBP 200601605 | 37.6 ppb |
| 2021-03-18 | DBP 200610316 | 31.1 ppb |
| 2021-03-18 | DBP 200610317 | 13.8 ppb |
| 2021-03-18 | DBP 200610318 | 11.4 ppb |
| 2021-03-18 | DBP 200610319 | 26.2 ppb |
| 2021-03-18 | DBP 200610320 | 58.1 ppb |
| 2021-03-18 | DBP 200610321 | 25.0 ppb |
| 2021-03-18 | DBP 200610322 | 39.0 ppb |
| 2021-03-18 | DBP 200610323 | 11.2 ppb |
| 2021-06-17 | DBP 200621341 | 46.1 ppb |
| 2021-06-17 | DBP 200621342 | 25.9 ppb |
| 2021-06-17 | DBP 200621343 | 48.5 ppb |
| 2021-06-17 | DBP 200621344 | 52.4 ppb |
| 2021-06-17 | DBP 200621345 | 18.7 ppb |
| 2021-06-17 | DBP 200621346 | 19.7 ppb |
| 2021-06-17 | DBP 200621347 | 41.2 ppb |
| 2021-06-17 | DBP 200621348 | 42.0 ppb |
| 2021-09-14 | 272610 | 34.8 ppb |
| 2021-09-14 | 272612 | 21.1 ppb |
| 2021-09-14 | 272616 | 48.4 ppb |
| 2021-09-14 | 272624 | 21.2 ppb |
| 2021-09-15 | 272620X | 40.0 ppb |
| 2021-09-15 | 272618 | 40.1 ppb |
| 2021-09-15 | 272622 | 51.0 ppb |
| 2021-09-15 | 272614 | 21.8 ppb |
| 2021-12-13 | 277826X | 8.36 ppb |
| 2021-12-13 | 277826XX | 24.0 ppb |
| 2021-12-14 | 277831X | 18.6 ppb |
| 2021-12-14 | 277828XX | 33.0 ppb |
| 2021-12-14 | 277830XX | 29.5 ppb |
| 2021-12-14 | 277832XX | 35.2 ppb |
| 2021-12-14 | 277834XX | 45.8 ppb |
| 2021-12-14 | 277836XX | 38.6 ppb |
| 2021-12-14 | 277822XX | 42.0 ppb |
| 2021-12-14 | 277824XX | 18.7 ppb |
| 2021-12-14 | 277822 | 42.1 ppb |
| 2021-12-14 | 277824X | 18.8 ppb |
| 2021-12-14 | 277828X | 32.6 ppb |
| 2021-12-14 | 277830X | 29.5 ppb |
| 2021-12-14 | 277832X | 35.3 ppb |
| 2021-12-14 | 277836X | 38.6 ppb |
| 2021-12-14 | 277834X | 15.9 ppb |
| 2022-03-08 | 281741 | 36.0 ppb |
| 2022-03-08 | 281743 | 31.0 ppb |
| 2022-03-08 | 281738 | 28.6 ppb |
| 2022-03-08 | 281739 | 17.0 ppb |
| 2022-03-09 | 281740 | 16.9 ppb |
| 2022-03-09 | 281744 | 31.0 ppb |
| 2022-03-10 | 281745 | 16.9 ppb |
| 2022-03-10 | 281742 | 29.2 ppb |
| 2022-06-14 | 288296 | 57.1 ppb |
| 2022-06-14 | 288298 | 56.3 ppb |
| 2022-06-14 | 288302 | 58.4 ppb |
| 2022-06-14 | 288304 | 34.7 ppb |
| 2022-06-15 | 288300 | 52.0 ppb |
| 2022-06-15 | 288290 | 48.6 ppb |
| 2022-06-15 | 288292 | 28.5 ppb |
| 2022-06-15 | 288294 | 29.0 ppb |
| 2022-09-14 | 296289 | 33.0 ppb |
| 2022-09-15 | 296291 | 4.40 ppb |
| 2022-09-15 | 296293 | 48.0 ppb |
| 2022-09-15 | 296295 | 48.8 ppb |
| 2022-09-15 | 296297 | 48.0 ppb |
| 2022-09-15 | 296299 | 45.0 ppb |
| 2022-09-15 | 296301 | 31.7 ppb |
| 2022-09-15 | 296307 | 53.0 ppb |
| 2022-12-13 | 303027 | 23.6 ppb |
| 2022-12-13 | 303030 | 30.7 ppb |
| 2022-12-13 | 303034 | 23.6 ppb |
| 2022-12-13 | 303036 | 29.8 ppb |
| 2022-12-13 | 303038 | 9.40 ppb |
| 2022-12-14 | 303032 | 27.9 ppb |
| 2022-12-15 | 303025 | 19.8 ppb |
| 2022-12-15 | 303023 | 10.5 ppb |
| 2023-03-06 | 307813 | 23.8 ppb |
| 2023-03-07 | 307811 | 30.0 ppb |
| 2023-03-07 | 307812 | 13.2 ppb |
| 2023-03-07 | 307817 | 26.0 ppb |
| 2023-03-07 | 307818 | 14.4 ppb |
| 2023-03-07 | 307814 | 16.5 ppb |
| 2023-03-07 | 307816 | 17.1 ppb |
| 2023-03-08 | 307815 | 18.1 ppb |
| 2023-06-06 | N3F0423-01PPS | 51.0 ppb |
| 2023-06-06 | N3F0423-03PPS | 32.0 ppb |
| 2023-06-06 | N3F0423-06PPS | 54.0 ppb |
| 2023-06-06 | N3F0423-08PPS | 25.0 ppb |
| 2023-06-06 | N3F0423-03 | 32.0 ppb |
| 2023-06-06 | N3F0423-06 | 54.0 ppb |
| 2023-06-06 | N3F0423-08 | 25.0 ppb |
| 2023-06-06 | N3F0423-01 | 51.0 ppb |
| 2023-06-07 | N3F0423-02 | 31.0 ppb |
| 2023-06-07 | N3F0423-07 | 52.0 ppb |
| 2023-06-07 | N3F0423-04 | 50.0 ppb |
| 2023-06-08 | N3F0423-05 | 45.0 ppb |
| 2023-09-12 | CO99982 | 54.7 ppb |
| 2023-09-12 | CO99983 | 38.3 ppb |
| 2023-09-12 | CO99989 | 34.1 ppb |
| 2023-09-13 | CO99986 | 64.7 ppb |
| 2023-09-13 | CO99987 | 59.5 ppb |
| 2023-09-13 | CO99988 | 71.8 ppb |
| 2023-09-14 | CO99984 | 32.1 ppb |
| 2023-09-14 | CO99985 | 61.4 ppb |
| 2023-12-11 | CP68213 | 28.2 ppb |
| 2023-12-12 | CP68214 | 44.2 ppb |
| 2023-12-12 | CP68211 | 54.8 ppb |
| 2023-12-12 | CP68212 | 25.9 ppb |
| 2023-12-12 | CP68216 | 44.4 ppb |
| 2023-12-12 | CP68217 | 56.2 ppb |
| 2023-12-12 | CP68218 | 32.8 ppb |
| 2023-12-13 | CP68215 | 35.4 ppb |