Total trihalomethanes (TTHMs)
Avon Water Company
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 | 6.43 ppb | 17 | 16 | ND - 12.0 ppb |
| 2019 | 7.84 ppb | 16 | 15 | ND - 18.0 ppb |
| 2020 | 9.08 ppb | 16 | 16 | 2.40 ppb - 18.6 ppb |
| 2021 | 9.84 ppb | 16 | 16 | 1.70 ppb - 22.8 ppb |
| 2022 | 8.89 ppb | 16 | 16 | 0.650 ppb - 21.3 ppb |
| 2023 | 10.3 ppb | 16 | 16 | 1.57 ppb - 19.1 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 |
|---|---|---|
| 2018-01-24 | D8A1669-02VOC | 5.50 ppb |
| 2018-01-24 | D8A1669-03VOC | 7.20 ppb |
| 2018-01-24 | D8A1669-04VOC | 3.50 ppb |
| 2018-01-24 | D8A1669-01VOC | 6.00 ppb |
| 2018-04-25 | D8D2151-08VOC | 0.800 ppb |
| 2018-04-25 | D8D2151-09VOC | 12.0 ppb |
| 2018-04-25 | D8D2151-10VOC | 7.10 ppb |
| 2018-04-25 | D8D2151-11VOC | 9.90 ppb |
| 2018-07-26 | CA98746 | 10.7 ppb |
| 2018-07-26 | CA98745 | 5.03 ppb |
| 2018-07-26 | CA98744 | 10.6 ppb |
| 2018-07-26 | CA98743 | 0.630 ppb |
| 2018-10-09 | DBP 200508664 | 6.60 ppb |
| 2018-10-09 | DBP 200508665 | 6.10 ppb |
| 2018-10-09 | DBP 200508676 | 7.80 ppb |
| 2018-10-09 | DBP 200508678 | 9.90 ppb |
| 2018-10-09 | VOC1 200508699 | ND |
| 2019-01-08 | DBP 200518131 | 4.90 ppb |
| 2019-01-08 | DBP 200518132 | ND |
| 2019-01-08 | DBP 200518133 | 4.40 ppb |
| 2019-01-08 | DBP 200518135 | 3.60 ppb |
| 2019-04-11 | DBP 200528269 | 7.70 ppb |
| 2019-04-11 | DBP 200528270 | 8.00 ppb |
| 2019-04-11 | DBP 200528268 | 12.2 ppb |
| 2019-04-11 | DBP 200528267 | 5.80 ppb |
| 2019-07-02 | DBP 200538992 | 2.70 ppb |
| 2019-07-02 | DBP 200538993 | 15.0 ppb |
| 2019-07-02 | DBP 200538995 | 8.50 ppb |
| 2019-07-02 | DBP 200538996 | 11.9 ppb |
| 2019-10-03 | DBP 200551429 | 2.60 ppb |
| 2019-10-03 | DBP 200551430 | 18.0 ppb |
| 2019-10-03 | DBP 200551431 | 8.40 ppb |
| 2019-10-03 | DBP 200551432 | 11.7 ppb |
| 2020-01-09 | DBP 200562757 | 6.90 ppb |
| 2020-01-09 | DBP 200562758 | 6.20 ppb |
| 2020-01-09 | DBP 200562756 | 5.40 ppb |
| 2020-01-09 | DBP 200562755 | 2.40 ppb |
| 2020-04-16 | DBP 200572926 | 4.40 ppb |
| 2020-04-16 | DBP 200572927 | 8.90 ppb |
| 2020-04-16 | DBP 200572928 | 8.20 ppb |
| 2020-04-16 | DBP 200572929 | 16.1 ppb |
| 2020-07-20 | DBP 200583413 | 2.60 ppb |
| 2020-07-20 | DBP 200583414 | 12.9 ppb |
| 2020-07-20 | DBP 200583415 | 6.70 ppb |
| 2020-07-20 | DBP 200583416 | 15.6 ppb |
| 2020-10-21 | DBP 200595047 | 18.6 ppb |
| 2020-10-21 | DBP 200595046 | 18.2 ppb |
| 2020-10-21 | DBP 200595044 | 2.50 ppb |
| 2020-10-21 | DBP 200595045 | 9.70 ppb |
| 2021-01-07 | DBP 200603402 | 6.10 ppb |
| 2021-01-07 | DBP 200603404 | 5.90 ppb |
| 2021-01-07 | DBP 200603405 | 15.9 ppb |
| 2021-01-07 | DBP 200603406 | 16.4 ppb |
| 2021-04-15 | DBP 200613652 | 4.20 ppb |
| 2021-04-15 | DBP 200613653 | 8.00 ppb |
| 2021-04-15 | DBP 200613654 | 9.80 ppb |
| 2021-04-15 | DBP 200613655 | 10.2 ppb |
| 2021-07-01 | DBP 200623336 | 21.7 ppb |
| 2021-07-01 | DBP 200623338 | 22.8 ppb |
| 2021-07-01 | DBP 200623335 | 3.80 ppb |
| 2021-07-01 | DBP 200623334 | 1.70 ppb |
| 2021-10-12 | H300079406 300079410 | 7.20 ppb |
| 2021-10-12 | H300079407 300079412 | 11.3 ppb |
| 2021-10-12 | H300079408 300079414 | 10.7 ppb |
| 2021-10-12 | H300079409 300079416 | 1.70 ppb |
| 2022-01-14 | CK17779 | 3.22 ppb |
| 2022-01-14 | CK17780 | 5.21 ppb |
| 2022-01-14 | CK17781 | 6.85 ppb |
| 2022-01-18 | CK17774 | 1.31 ppb |
| 2022-04-15 | CL11169 | 14.3 ppb |
| 2022-04-15 | CL11168 | 8.60 ppb |
| 2022-04-15 | CL11166 | 6.76 ppb |
| 2022-04-15 | CL11167 | 8.10 ppb |
| 2022-07-08 | CL75309 | 0.650 ppb |
| 2022-07-08 | CL75310 | 21.3 ppb |
| 2022-07-08 | CL75311 | 10.5 ppb |
| 2022-07-08 | CL75312 | 9.80 ppb |
| 2022-10-21 | CM69248 | 8.00 ppb |
| 2022-10-21 | CM69249 | 10.5 ppb |
| 2022-10-21 | CM69250 | 13.1 ppb |
| 2022-10-21 | CM69251 | 14.0 ppb |
| 2023-01-11 | CN21964 | 4.30 ppb |
| 2023-01-12 | CN24190 | 12.7 ppb |
| 2023-01-12 | CN24189 | 12.9 ppb |
| 2023-01-12 | CN24188 | 9.80 ppb |
| 2023-04-14 | CN85862 | 5.85 ppb |
| 2023-04-14 | CN85863 | 8.20 ppb |
| 2023-04-14 | CN85864 | 8.30 ppb |
| 2023-04-14 | CN85865 | 7.80 ppb |
| 2023-07-13 | CO53041 | 1.57 ppb |
| 2023-07-13 | CO53042 | 8.50 ppb |
| 2023-07-13 | CO53043 | 12.0 ppb |
| 2023-07-25 | CO58855 | 14.6 ppb |
| 2023-10-04 | CP17807 | 5.48 ppb |
| 2023-10-04 | CP17808 | 19.1 ppb |
| 2023-10-04 | CP17809 | 17.7 ppb |
| 2023-10-04 | CP17810 | 15.9 ppb |