Know Your Environment. Protect Your Health.

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.

Click here to read more about disinfection byproducts.

 

196

Samples

6

Samples exceeding legal limit (MCL)

196

Samples exceeding
health guidelines

Testing results - average by year

 
YearAverage resultSamples takenDetectionsRange of results
201853.0 ppb353521.8 ppb - 103.4 ppb
201940.8 ppb323216.3 ppb - 70.5 ppb
202040.2 ppb333310.9 ppb - 79.1 ppb
202143.6 ppb32329.50 ppb - 82.3 ppb
202246.0 ppb323220.7 ppb - 72.4 ppb
202343.6 ppb323218.9 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
2018-02-01BZ83504TTHM41.3 ppb
2018-02-01BZ83505TTHM56.7 ppb
2018-02-01BZ83506TTHM52.5 ppb
2018-02-01BZ83507TTHM63.8 ppb
2018-02-01BZ83508TTHM25.8 ppb
2018-02-01BZ83509TTHM28.8 ppb
2018-02-01BZ83510TTHM26.1 ppb
2018-02-21BZ93283TTHM33.0 ppb
2018-05-03CA41161TTHM39.8 ppb
2018-05-03CA41162TTHM65.6 ppb
2018-05-03CA41163TTHM58.4 ppb
2018-05-03CA41164TTHM72.0 ppb
2018-05-03CA41165TTHM21.8 ppb
2018-05-03CA41166TTHM27.7 ppb
2018-05-03CA41167TTHM29.0 ppb
2018-05-03D8E0468-01VOC67.0 ppb
2018-05-15CA48118TTHM45.6 ppb
2018-08-02CB0402048.3 ppb
2018-08-02CB04021103.4 ppb
2018-08-02CB0402269.5 ppb
2018-08-02CB0402383.4 ppb
2018-08-02CB0402438.5 ppb
2018-08-02CB0402554.6 ppb
2018-08-02CB0402655.5 ppb
2018-08-06CB0584062.2 ppb
2018-08-10DBP 20050203184.0 ppb
2018-08-10CB0915490.0 ppb
2018-11-01DBP 20051113358.6 ppb
2018-11-01DBP 20051113474.3 ppb
2018-11-01DBP 20051113577.1 ppb
2018-11-01DBP 20051113683.9 ppb
2018-11-01DBP 20051113734.7 ppb
2018-11-01DBP 20051113822.1 ppb
2018-11-01DBP 20051113926.9 ppb
2018-11-05DBP 20051138934.5 ppb
2019-02-07DBP 20052108316.3 ppb
2019-02-07DBP 20052108443.6 ppb
2019-02-07DBP 20052108517.2 ppb
2019-02-07DBP 20052108639.5 ppb
2019-02-07DBP 20052108717.8 ppb
2019-02-07DBP 20052108847.2 ppb
2019-02-07DBP 20052108935.8 ppb
2019-02-11DBP 20052125622.9 ppb
2019-05-09DBP 20053157534.5 ppb
2019-05-09DBP 20053157660.1 ppb
2019-05-09DBP 20053157756.2 ppb
2019-05-09DBP 20053158264.7 ppb
2019-05-09DBP 20053158421.3 ppb
2019-05-09DBP 20053158619.3 ppb
2019-05-09DBP 20053158719.1 ppb
2019-05-13DBP 20053183730.0 ppb
2019-08-01DBP 20054272238.1 ppb
2019-08-01DBP 20054272351.6 ppb
2019-08-01DBP 20054272438.9 ppb
2019-08-01DBP 20054272569.1 ppb
2019-08-01DBP 20054272640.8 ppb
2019-08-01DBP 20054272728.3 ppb
2019-08-01DBP 20054272826.4 ppb
2019-08-13DBP 20054475850.5 ppb
2019-11-07DBP 20055582867.1 ppb
2019-11-07DBP 20055583070.5 ppb
2019-11-07DBP 20055583163.8 ppb
2019-11-07DBP 20055583270.1 ppb
2019-11-07DBP 20055583348.8 ppb
2019-11-07DBP 20055583432.2 ppb
2019-11-07DBP 20055583526.5 ppb
2019-11-18DBP 20055700436.1 ppb
2020-01-06DBP 20056166527.9 ppb
2020-02-06DBP 20056535754.9 ppb
2020-02-06DBP 20056535850.0 ppb
2020-02-06DBP 20056535941.9 ppb
2020-02-06DBP 20056536034.8 ppb
2020-02-06DBP 20056536121.5 ppb
2020-02-06DBP 20056536215.8 ppb
2020-02-07DBP 20056564063.4 ppb
2020-02-07DBP 20056564126.1 ppb
2020-05-07DBP 20057517158.4 ppb
2020-05-07DBP 20057517379.1 ppb
2020-05-07DBP 20057517525.3 ppb
2020-05-07DBP 20057517621.1 ppb
2020-05-07DBP 20057517735.9 ppb
2020-05-08DBP 20057517439.0 ppb
2020-05-08DBP 20057517244.3 ppb
2020-05-08DBP 20057517072.8 ppb
2020-08-06DBP 20058574439.0 ppb
2020-08-06DBP 20058575057.8 ppb
2020-08-06DBP 20058575349.9 ppb
2020-08-06DBP 20058575451.1 ppb
2020-08-07DBP 20058575566.8 ppb
2020-08-07DBP 20058575628.8 ppb
2020-08-07DBP 20058575731.1 ppb
2020-08-07DBP 20058575849.1 ppb
2020-11-05DBP 20059735619.1 ppb
2020-11-05DBP 20059735764.4 ppb
2020-11-05DBP 20059735832.4 ppb
2020-11-05DBP 20059735912.4 ppb
2020-11-05DBP 20059736010.9 ppb
2020-11-05DBP 20059736118.9 ppb
2020-11-12DBP 20059820645.3 ppb
2020-11-12DBP 20059821036.6 ppb
2021-02-11DBP 20060689513.7 ppb
2021-02-11DBP 20060689619.1 ppb
2021-02-11DBP 2006069079.50 ppb
2021-02-12DBP 20060691121.6 ppb
2021-02-16DBP 20060691249.0 ppb
2021-02-17DBP 20060711227.8 ppb
2021-02-22DBP 20060745913.0 ppb
2021-02-23DBP 20060764533.6 ppb
2021-05-13DBP 20061723940.7 ppb
2021-05-14DBP 20061723653.1 ppb
2021-05-14DBP 20061723726.5 ppb
2021-05-14DBP 20061723821.0 ppb
2021-05-20DBP 20061831668.9 ppb
2021-05-20DBP 20061831728.6 ppb
2021-05-20DBP 20061831956.5 ppb
2021-05-20DBP 20061832160.8 ppb
2021-08-12DBP 20062875658.0 ppb
2021-08-12DBP 20062875731.0 ppb
2021-08-12DBP 20062875876.5 ppb
2021-08-12DBP 20062875934.8 ppb
2021-08-12DBP 20062876041.8 ppb
2021-08-12DBP 20062876153.9 ppb
2021-08-25DBP 20062981571.7 ppb
2021-08-25DBP 20062981676.8 ppb
2021-11-04D300098348 30009835746.6 ppb
2021-11-04D300098349 30009835926.2 ppb
2021-11-04D300098350 30009836175.7 ppb
2021-11-04D300098351 30009836321.7 ppb
2021-11-04D300098352 30009836534.8 ppb
2021-11-05D300098353 30009836754.0 ppb
2021-11-05D300098354 30009836982.3 ppb
2021-11-05D300098355 30009837165.0 ppb
2022-02-03CK2975235.0 ppb
2022-02-03CK2975325.0 ppb
2022-02-03CK2975467.1 ppb
2022-02-03CK2975528.0 ppb
2022-02-03CK2975640.0 ppb
2022-02-03CK2975741.1 ppb
2022-02-03CK2975854.6 ppb
2022-02-04CK3148972.4 ppb
2022-05-12CL3151336.9 ppb
2022-05-12CL3151466.1 ppb
2022-05-12CL3151528.0 ppb
2022-05-12CL3151644.1 ppb
2022-05-12CL3151728.2 ppb
2022-05-13CL3151850.8 ppb
2022-05-13CL3151948.8 ppb
2022-05-13CL3152049.7 ppb
2022-08-04CL9896364.3 ppb
2022-08-04CL9896454.5 ppb
2022-08-04CL9896566.5 ppb
2022-08-05CL9896662.7 ppb
2022-08-05CL9896759.5 ppb
2022-08-05CL9896861.5 ppb
2022-08-05CL9896967.6 ppb
2022-08-05CL9897047.2 ppb
2022-11-17CM9028340.5 ppb
2022-11-17CM9028420.7 ppb
2022-11-17CM9028549.1 ppb
2022-11-17CM9028625.2 ppb
2022-11-17CM9028739.2 ppb
2022-11-17CM9028831.3 ppb
2022-11-17CM9028928.6 ppb
2022-11-18CM9029037.7 ppb
2023-02-02CN3707718.9 ppb
2023-02-02CN3707827.4 ppb
2023-02-02CN3707939.5 ppb
2023-02-02CN3708019.0 ppb
2023-02-02CN3708128.8 ppb
2023-02-02CN3708228.9 ppb
2023-02-02CN3708337.3 ppb
2023-02-02CN3708434.1 ppb
2023-05-12CO0629430.9 ppb
2023-05-12CO0629572.6 ppb
2023-05-12CO0629633.6 ppb
2023-05-12CO0629750.7 ppb
2023-05-12CO0629857.0 ppb
2023-05-12CO0629959.3 ppb
2023-05-18CO0938651.7 ppb
2023-05-18CO0938761.8 ppb
2023-08-10CO7337639.5 ppb
2023-08-10CO7337770.9 ppb
2023-08-10CO7337876.7 ppb
2023-08-11CO7337939.0 ppb
2023-08-11CO7338050.1 ppb
2023-08-11CO7338156.2 ppb
2023-08-11CO7338257.3 ppb
2023-08-11CO7338379.5 ppb
2023-11-16CP5044941.5 ppb
2023-11-16CP5045032.2 ppb
2023-11-16CP5045148.9 ppb
2023-11-16CP5045226.6 ppb
2023-11-16CP5045323.2 ppb
2023-11-16CP5045445.7 ppb
2023-11-16CP5045520.9 ppb
2023-11-17CP5045634.2 ppb