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.

MORE ABOUT THIS CONTAMINANT

197

Samples

Samples exceeding legal limit (MCL)

197

Samples exceeding
health guidelines

Testing results - average by year

Year	Average result	Samples taken	Detections	Range of results
2014	48.3 ppb	35	35	19.0 ppb - 96.0 ppb
2015	42.7 ppb	32	32	20.0 ppb - 75.0 ppb
2016	42.9 ppb	32	32	19.0 ppb - 78.0 ppb
2017	45.2 ppb	32	32	29.2 ppb - 76.0 ppb
2018	43.6 ppb	32	32	14.5 ppb - 91.7 ppb
2019	32.9 ppb	34	34	13.7 ppb - 55.7 ppb

ppb = parts per billion

State and national drinking water standards and health guidelines

EWG Health Guideline 0.15 ppb

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
2014-03-11	E403C94-2TTHM	34.0 ppb
2014-03-11	E403C94-4TTHM	38.0 ppb
2014-03-11	E403C94-7TTHM	35.0 ppb
2014-03-12	E403C94-1TTHM	44.0 ppb
2014-03-13	E403C94-6TTHM	19.0 ppb
2014-03-14	E403C94-8TTHM	26.0 ppb
2014-03-17	E403C94-3TTHM	26.0 ppb
2014-03-18	E403C94-5TTHM	20.0 ppb
2014-06-10	E406G56-4TTHM	65.0 ppb
2014-06-10	E406G56-6TTHM	51.0 ppb
2014-06-11	E406G56-1TTHM	69.0 ppb
2014-06-12	E406G56-2TTHM	51.0 ppb
2014-06-12	E406G56-7TTHM	63.0 ppb
2014-06-12	E406G56-8TTHM	40.0 ppb
2014-06-13	E406G56-5TTHM	52.0 ppb
2014-06-16	E406G56-3TTHM	33.0 ppb
2014-09-10	E409F66-1TTHM	70.0 ppb
2014-09-11	E409F66-4TTHM	86.0 ppb
2014-09-11	E409F66-6TTHM	58.0 ppb
2014-09-12	E409F66-2TTHM	57.0 ppb
2014-09-12	E409F66-8TTHM	55.0 ppb
2014-09-15	E409F66-3TTHM	54.0 ppb
2014-09-23	E409M19-1TTHM	96.0 ppb
2014-09-23	E409M19-2TTHM	61.0 ppb
2014-09-23	E409M19-3TTHM	85.0 ppb
2014-09-30	E409T37-2TTHM	58.0 ppb
2014-09-30	E410021-1TTHM	75.0 ppb
2014-12-12	E412D88-1TTHM	50.0 ppb
2014-12-12	E412D88-7TTHM	30.0 ppb
2014-12-12	E412D88-8TTHM	28.0 ppb
2014-12-15	E412D88-2TTHM	20.0 ppb
2014-12-15	E412D88-3TTHM	34.0 ppb
2014-12-15	E412D88-4TTHM	54.0 ppb
2014-12-15	E412D88-6TTHM	26.0 ppb
2014-12-16	E412D88-5TTHM	29.0 ppb
2015-03-12	E503B60-2TTHM	34.0 ppb
2015-03-12	E503B60-5TTHM	33.0 ppb
2015-03-13	E503B60-1TTHM	45.0 ppb
2015-03-13	E503B60-6TTHM	24.0 ppb
2015-03-13	E503B60-4TTHM	39.0 ppb
2015-03-16	E503B60-3TTHM	30.0 ppb
2015-03-25	E503J77-1TTHM	28.0 ppb
2015-03-26	E503J77-2TTHM	31.0 ppb
2015-06-11	E506H99-5TTHM	35.0 ppb
2015-06-12	E506H99-7TTHM	52.0 ppb
2015-06-12	E506H99-8TTHM	25.0 ppb
2015-06-15	E506H99-4TTHM	42.0 ppb
2015-06-15	E506H99-1TTHM	52.0 ppb
2015-06-15	E506H99-2TTHM	29.0 ppb
2015-06-15	E506H99-3TTHM	27.0 ppb
2015-06-16	E506H99-6TTHM	39.0 ppb
2015-09-18	E509O88-8TTHM	47.0 ppb
2015-09-18	E509O88-6TTHM	65.0 ppb
2015-09-21	E509O88-1TTHM	73.0 ppb
2015-09-21	E509O88-2TTHM	61.0 ppb
2015-09-21	E509O88-3TTHM	44.0 ppb
2015-09-22	E509O88-5TTHM	74.0 ppb
2015-09-29	E509W38-2TTHM	75.0 ppb
2015-09-29	E509W38-1TTHM	66.0 ppb
2015-12-17	E512K74-1-16TTHM	51.0 ppb
2015-12-17	E512K74-2-17TTHM	20.0 ppb
2015-12-17	E512K74-7-15TTHM	56.0 ppb
2015-12-17	E512K74-5-19TTHM	39.0 ppb
2015-12-17	E512K74-4-18TTHM	43.0 ppb
2015-12-18	E512K74-6-20TTHM	27.0 ppb
2015-12-18	E512K74-8-04TTHM	30.0 ppb
2015-12-21	E512K74-3-03TTHM	31.0 ppb
2016-03-09	E603E03-1-16TTHM	51.0 ppb
2016-03-09	E603E03-4-18TTHM	43.0 ppb
2016-03-10	E603E03-5-19TTHM	29.0 ppb
2016-03-10	E603E03-6-20TTHM	30.0 ppb
2016-03-10	E603E03-7-15TTHM	38.0 ppb
2016-03-10	E603E03-2-17TTHM	19.0 ppb
2016-03-11	E603E03-8-04TTHM	28.0 ppb
2016-03-14	E603E03-3-03TTHM	33.0 ppb
2016-06-16	E606O13-1-16TTHM	60.0 ppb
2016-06-16	E606O13-2-17TTHM	36.0 ppb
2016-06-16	E606O13-4-18TTHM	50.0 ppb
2016-06-16	E606O13-5-19TTHM	37.0 ppb
2016-06-16	E606O13-6-20TTHM	47.0 ppb
2016-06-16	E606O13-8-04TTHM	38.0 ppb
2016-06-20	E606O13-7-15TTHM	52.0 ppb
2016-06-20	E606O13-3-03TTHM	32.0 ppb
2016-09-08	188687CH	54.5 ppb
2016-09-09	188691CH	43.2 ppb
2016-09-13	188689CH	78.0 ppb
2016-09-13	188677CH	46.2 ppb
2016-09-13	188679CH	39.2 ppb
2016-09-13	188681CH	40.3 ppb
2016-09-13	188683CH	57.1 ppb
2016-09-14	188685CH	63.2 ppb
2016-12-12	192764CH	38.8 ppb
2016-12-13	192766CH	61.6 ppb
2016-12-13	192768CH	42.9 ppb
2016-12-13	192754CH	41.6 ppb
2016-12-13	192756CH	33.9 ppb
2016-12-13	192760CH	39.1 ppb
2016-12-13	192762CH	31.1 ppb
2016-12-14	192758CH	40.3 ppb
2017-03-09	196059GE	46.7 ppb
2017-03-09	196061GE	43.5 ppb
2017-03-09	196065GE	36.3 ppb
2017-03-13	196063GE	47.5 ppb
2017-03-14	196069GE	40.7 ppb
2017-03-15	196071GE	39.8 ppb
2017-03-15	196073GE	45.9 ppb
2017-03-15	196067GE	33.6 ppb
2017-06-13	200345GE	46.0 ppb
2017-06-13	200351GE	51.3 ppb
2017-06-14	200349GE	43.8 ppb
2017-06-14	200341GE	36.1 ppb
2017-06-14	200339GE	42.6 ppb
2017-06-15	200343GE	34.4 ppb
2017-06-15	200353GE	47.6 ppb
2017-06-15	200347GE	39.1 ppb
2017-09-12	204472GE	55.7 ppb
2017-09-12	204474GE	46.2 ppb
2017-09-12	204478GE	54.8 ppb
2017-09-12	204484GE	76.0 ppb
2017-09-12	204486GE	55.6 ppb
2017-09-13	204480GE	56.0 ppb
2017-09-13	204482GE	51.7 ppb
2017-09-13	204476GE	47.1 ppb
2017-12-11	208503GE	49.2 ppb
2017-12-11	208505GE	37.5 ppb
2017-12-12	208501GE	35.5 ppb
2017-12-12	208507GE	29.2 ppb
2017-12-12	208509GE	46.6 ppb
2017-12-12	208511GE	45.4 ppb
2017-12-12	208513GE	44.2 ppb
2017-12-12	208499GE	40.9 ppb
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