Know Your Environment. Protect Your Health.

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.

Click here to read more about disinfection byproducts.

 

207

Samples

2

Samples exceeding legal limit (MCL)

207

Samples exceeding
health guidelines

Testing results - average by year

 
YearAverage resultSamples takenDetectionsRange of results
201843.6 ppb323214.5 ppb - 91.7 ppb
201932.9 ppb343413.7 ppb - 55.7 ppb
202037.5 ppb323215.1 ppb - 69.7 ppb
202131.6 ppb41418.36 ppb - 58.1 ppb
202233.1 ppb32324.40 ppb - 58.4 ppb
202338.9 ppb363613.2 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
2018-03-14211584GE39.8 ppb
2018-03-14211586GE33.7 ppb
2018-03-14211588GE39.3 ppb
2018-03-14211590GE38.8 ppb
2018-03-14211598GE38.5 ppb
2018-03-15211592GE32.2 ppb
2018-03-15211594GE37.1 ppb
2018-03-15211596GE39.4 ppb
2018-06-19215736GE42.7 ppb
2018-06-19215738GE36.9 ppb
2018-06-19215742GE45.5 ppb
2018-06-19215744GE46.2 ppb
2018-06-19215750GE41.8 ppb
2018-06-20215746GE47.8 ppb
2018-06-20215748GE53.0 ppb
2018-06-20215740GE40.4 ppb
2018-09-14DBP 20050548435.3 ppb
2018-09-14DBP 20050548642.7 ppb
2018-09-14DBP 20050549174.0 ppb
2018-09-14DBP 20050549363.5 ppb
2018-09-14DBP 20050549591.7 ppb
2018-09-14DBP 20050549746.1 ppb
2018-09-14DBP 20050549969.6 ppb
2018-09-17DBP 20050565881.3 ppb
2018-12-14DBP 20051609337.9 ppb
2018-12-14DBP 20051609414.5 ppb
2018-12-14DBP 20051609519.7 ppb
2018-12-14DBP 20051609633.5 ppb
2018-12-14DBP 20051609740.9 ppb
2018-12-14DBP 20051609816.7 ppb
2018-12-14DBP 20051609946.7 ppb
2018-12-14DBP 20051610027.8 ppb
2019-03-14DBP 20052476037.1 ppb
2019-03-14DBP 20052476115.9 ppb
2019-03-14DBP 20052476222.5 ppb
2019-03-14DBP 20052476340.7 ppb
2019-03-14DBP 20052476419.8 ppb
2019-03-14DBP 20052476525.7 ppb
2019-03-14DBP 20052476630.7 ppb
2019-03-14DBP 20052476718.8 ppb
2019-06-20DBP 20053726545.8 ppb
2019-06-20DBP 20053726621.8 ppb
2019-06-20DBP 20053726720.2 ppb
2019-06-20DBP 20053726851.5 ppb
2019-06-20DBP 20053726944.0 ppb
2019-06-20DBP 20053727041.8 ppb
2019-06-20DBP 20053727155.7 ppb
2019-06-20DBP 20053727229.9 ppb
2019-08-15VOC1 20054512131.5 ppb
2019-08-15VOC1 20054512231.4 ppb
2019-09-19DBP 20054961244.9 ppb
2019-09-19DBP 20054961321.9 ppb
2019-09-19DBP 20054961425.3 ppb
2019-09-19DBP 20054961547.5 ppb
2019-09-19DBP 20054961647.6 ppb
2019-09-19DBP 20054961748.8 ppb
2019-09-19DBP 20054961852.9 ppb
2019-09-19DBP 20054961936.5 ppb
2019-12-19DBP 20056092634.1 ppb
2019-12-19DBP 20056092714.4 ppb
2019-12-19DBP 20056092913.7 ppb
2019-12-19DBP 20056093024.7 ppb
2019-12-19DBP 20056093136.0 ppb
2019-12-19DBP 20056093233.9 ppb
2019-12-19DBP 20056093419.3 ppb
2019-12-19DBP 20056093532.7 ppb
2020-03-19DBP 20056997635.4 ppb
2020-03-19DBP 20056997720.0 ppb
2020-03-19DBP 20056997825.1 ppb
2020-03-19DBP 20056997953.4 ppb
2020-03-19DBP 20056998038.7 ppb
2020-03-19DBP 20056998119.8 ppb
2020-03-19DBP 20056998244.5 ppb
2020-03-19DBP 20056998324.9 ppb
2020-06-18DBP 20057979446.5 ppb
2020-06-18DBP 20057979525.1 ppb
2020-06-18DBP 20057979620.7 ppb
2020-06-18DBP 20057979751.3 ppb
2020-06-18DBP 20057979847.3 ppb
2020-06-18DBP 20057979922.9 ppb
2020-06-18DBP 20057980051.4 ppb
2020-06-18DBP 20057980127.8 ppb
2020-09-17DBP 20059066156.5 ppb
2020-09-17DBP 20059066234.8 ppb
2020-09-17DBP 20059066354.0 ppb
2020-09-17DBP 20059066469.7 ppb
2020-09-17DBP 20059066528.7 ppb
2020-09-17DBP 20059066624.1 ppb
2020-09-17DBP 20059066759.0 ppb
2020-09-17DBP 20059066853.3 ppb
2020-12-18DBP 20060159842.5 ppb
2020-12-18DBP 20060159915.9 ppb
2020-12-18DBP 20060160015.1 ppb
2020-12-18DBP 20060160127.6 ppb
2020-12-18DBP 20060160237.9 ppb
2020-12-18DBP 20060160343.9 ppb
2020-12-18DBP 20060160445.3 ppb
2020-12-18DBP 20060160537.6 ppb
2021-03-18DBP 20061031631.1 ppb
2021-03-18DBP 20061031713.8 ppb
2021-03-18DBP 20061031811.4 ppb
2021-03-18DBP 20061031926.2 ppb
2021-03-18DBP 20061032058.1 ppb
2021-03-18DBP 20061032125.0 ppb
2021-03-18DBP 20061032239.0 ppb
2021-03-18DBP 20061032311.2 ppb
2021-06-17DBP 20062134146.1 ppb
2021-06-17DBP 20062134225.9 ppb
2021-06-17DBP 20062134348.5 ppb
2021-06-17DBP 20062134452.4 ppb
2021-06-17DBP 20062134518.7 ppb
2021-06-17DBP 20062134619.7 ppb
2021-06-17DBP 20062134741.2 ppb
2021-06-17DBP 20062134842.0 ppb
2021-09-1427261034.8 ppb
2021-09-1427261221.1 ppb
2021-09-1427261648.4 ppb
2021-09-1427262421.2 ppb
2021-09-15272620X40.0 ppb
2021-09-1527261840.1 ppb
2021-09-1527262251.0 ppb
2021-09-1527261421.8 ppb
2021-12-13277826X8.36 ppb
2021-12-13277826XX24.0 ppb
2021-12-14277831X18.6 ppb
2021-12-14277828XX33.0 ppb
2021-12-14277830XX29.5 ppb
2021-12-14277832XX35.2 ppb
2021-12-14277834XX45.8 ppb
2021-12-14277836XX38.6 ppb
2021-12-14277822XX42.0 ppb
2021-12-14277824XX18.7 ppb
2021-12-1427782242.1 ppb
2021-12-14277824X18.8 ppb
2021-12-14277828X32.6 ppb
2021-12-14277830X29.5 ppb
2021-12-14277832X35.3 ppb
2021-12-14277836X38.6 ppb
2021-12-14277834X15.9 ppb
2022-03-0828174136.0 ppb
2022-03-0828174331.0 ppb
2022-03-0828173828.6 ppb
2022-03-0828173917.0 ppb
2022-03-0928174016.9 ppb
2022-03-0928174431.0 ppb
2022-03-1028174516.9 ppb
2022-03-1028174229.2 ppb
2022-06-1428829657.1 ppb
2022-06-1428829856.3 ppb
2022-06-1428830258.4 ppb
2022-06-1428830434.7 ppb
2022-06-1528830052.0 ppb
2022-06-1528829048.6 ppb
2022-06-1528829228.5 ppb
2022-06-1528829429.0 ppb
2022-09-1429628933.0 ppb
2022-09-152962914.40 ppb
2022-09-1529629348.0 ppb
2022-09-1529629548.8 ppb
2022-09-1529629748.0 ppb
2022-09-1529629945.0 ppb
2022-09-1529630131.7 ppb
2022-09-1529630753.0 ppb
2022-12-1330302723.6 ppb
2022-12-1330303030.7 ppb
2022-12-1330303423.6 ppb
2022-12-1330303629.8 ppb
2022-12-133030389.40 ppb
2022-12-1430303227.9 ppb
2022-12-1530302519.8 ppb
2022-12-1530302310.5 ppb
2023-03-0630781323.8 ppb
2023-03-0730781130.0 ppb
2023-03-0730781213.2 ppb
2023-03-0730781726.0 ppb
2023-03-0730781814.4 ppb
2023-03-0730781416.5 ppb
2023-03-0730781617.1 ppb
2023-03-0830781518.1 ppb
2023-06-06N3F0423-01PPS51.0 ppb
2023-06-06N3F0423-03PPS32.0 ppb
2023-06-06N3F0423-06PPS54.0 ppb
2023-06-06N3F0423-08PPS25.0 ppb
2023-06-06N3F0423-0332.0 ppb
2023-06-06N3F0423-0654.0 ppb
2023-06-06N3F0423-0825.0 ppb
2023-06-06N3F0423-0151.0 ppb
2023-06-07N3F0423-0231.0 ppb
2023-06-07N3F0423-0752.0 ppb
2023-06-07N3F0423-0450.0 ppb
2023-06-08N3F0423-0545.0 ppb
2023-09-12CO9998254.7 ppb
2023-09-12CO9998338.3 ppb
2023-09-12CO9998934.1 ppb
2023-09-13CO9998664.7 ppb
2023-09-13CO9998759.5 ppb
2023-09-13CO9998871.8 ppb
2023-09-14CO9998432.1 ppb
2023-09-14CO9998561.4 ppb
2023-12-11CP6821328.2 ppb
2023-12-12CP6821444.2 ppb
2023-12-12CP6821154.8 ppb
2023-12-12CP6821225.9 ppb
2023-12-12CP6821644.4 ppb
2023-12-12CP6821756.2 ppb
2023-12-12CP6821832.8 ppb
2023-12-13CP6821535.4 ppb