Total trihalomethanes (TTHMs)

City of Concord

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

193

Samples

Samples exceeding legal limit (MCL)

193

Samples exceeding
health guidelines

Testing results - average by year

Year	Average result	Samples taken	Detections	Range of results
2014	51.7 ppb	32	32	27.0 ppb - 81.0 ppb
2015	60.4 ppb	32	32	35.0 ppb - 103.0 ppb
2016	48.7 ppb	32	32	28.1 ppb - 107.3 ppb
2017	50.2 ppb	32	32	23.9 ppb - 108.7 ppb
2018	50.9 ppb	33	33	15.3 ppb - 94.8 ppb
2019	44.2 ppb	32	32	16.0 ppb - 77.0 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
2014-02-19	8221-021914-B01M	32.0 ppb
2014-02-19	8221-021914-B02M	36.0 ppb
2014-02-19	8221-021914-B03M	36.0 ppb
2014-02-19	8221-021914-B04M	36.0 ppb
2014-02-19	8221-021914-B05M	32.0 ppb
2014-02-19	8221-021914-B06M	30.0 ppb
2014-02-19	8221-021914-B07M	39.0 ppb
2014-02-19	8221-021914-B08M	27.0 ppb
2014-05-14	8221-051414-B01M	63.0 ppb
2014-05-14	8221-051414-B02M	67.0 ppb
2014-05-14	8221-051414-B03M	66.0 ppb
2014-05-14	8221-051414-B04M	72.0 ppb
2014-05-14	8221-051414-B05M	53.0 ppb
2014-05-14	8221-051414-B06M	66.0 ppb
2014-05-14	8221-051414-B07M	66.0 ppb
2014-05-14	8221-051414-B08M	54.0 ppb
2014-08-06	8221-080614-B01M	59.0 ppb
2014-08-06	8221-080614-B02M	75.0 ppb
2014-08-06	8221-080614-B03M	81.0 ppb
2014-08-06	8221-080614-B04M	80.0 ppb
2014-08-06	8221-080614-B05M	58.0 ppb
2014-08-06	8221-080614-B06M	66.0 ppb
2014-08-06	8221-080614-B07M	81.0 ppb
2014-08-06	8221-080614-B08M	48.0 ppb
2014-11-12	8221-111214-B01M	54.0 ppb
2014-11-12	8221-111214-B02M	38.0 ppb
2014-11-12	8221-111214-B03M	38.0 ppb
2014-11-12	8221-111214-B04M	36.0 ppb
2014-11-12	8221-111214-B05M	39.0 ppb
2014-11-12	8221-111214-B06M	41.0 ppb
2014-11-12	8221-111214-B07M	52.0 ppb
2014-11-12	8221-111214-B08M	33.0 ppb
2015-02-11		44.0 ppb
2015-02-11		36.0 ppb
2015-02-11		38.0 ppb
2015-02-11		35.0 ppb
2015-02-11		36.0 ppb
2015-02-11		35.0 ppb
2015-02-11		44.0 ppb
2015-02-11		45.0 ppb
2015-05-13		65.0 ppb
2015-05-13		103.0 ppb
2015-05-13		92.0 ppb
2015-05-13		73.0 ppb
2015-05-13		72.0 ppb
2015-05-13		79.0 ppb
2015-05-13		80.0 ppb
2015-05-20		89.0 ppb
2015-08-12		70.0 ppb
2015-08-12		61.2 ppb
2015-08-12		59.2 ppb
2015-08-12		71.9 ppb
2015-08-12		54.5 ppb
2015-08-12		95.3 ppb
2015-08-12		88.5 ppb
2015-08-12		60.2 ppb
2015-11-11		49.3 ppb
2015-11-11		43.6 ppb
2015-11-11		43.7 ppb
2015-11-11		58.3 ppb
2015-11-11		49.6 ppb
2015-11-11		41.6 ppb
2015-11-11		63.2 ppb
2015-11-11		58.2 ppb
2016-02-09	3398142	32.8 ppb
2016-02-09	3398143	34.0 ppb
2016-02-09	3398144	39.3 ppb
2016-02-09	3398145	37.1 ppb
2016-02-09	3398146	28.1 ppb
2016-02-09	3398147	35.3 ppb
2016-02-09	3398148	34.7 ppb
2016-02-09	3398149	42.3 ppb
2016-05-10	3445892	35.6 ppb
2016-05-10	3445893	34.4 ppb
2016-05-10	3445894	40.8 ppb
2016-05-10	3445895	40.3 ppb
2016-05-10	3445896	31.8 ppb
2016-05-10	3445897	44.6 ppb
2016-05-10	3445898	51.3 ppb
2016-05-10	3445891	47.9 ppb
2016-08-09	3516964	84.9 ppb
2016-08-09	3516965	56.2 ppb
2016-08-09	3516966	58.7 ppb
2016-08-09	3516967	74.6 ppb
2016-08-09	3516968	79.3 ppb
2016-08-09	3516969	62.7 ppb
2016-08-09	3516970	107.3 ppb
2016-08-09	3516971	64.7 ppb
2016-11-08	3582281	58.7 ppb
2016-11-08	3582282	41.7 ppb
2016-11-08	3582283	37.8 ppb
2016-11-08	3582284	37.9 ppb
2016-11-08	3582285	46.7 ppb
2016-11-08	3582286	30.3 ppb
2016-11-08	3582287	62.7 ppb
2016-11-08	3582288	44.1 ppb
2017-02-14	3638203	35.8 ppb
2017-02-14	3638204	25.2 ppb
2017-02-14	3638205	24.0 ppb
2017-02-14	3638206	25.7 ppb
2017-02-14	3638207	34.7 ppb
2017-02-14	3638208	23.9 ppb
2017-02-14	3638209	44.9 ppb
2017-02-14	3638210	35.8 ppb
2017-05-09	3691007	59.9 ppb
2017-05-09	3691008	35.5 ppb
2017-05-09	3691009	35.6 ppb
2017-05-09	3691010	47.8 ppb
2017-05-09	3691011	58.1 ppb
2017-05-09	3691012	37.9 ppb
2017-05-09	3691013	74.5 ppb
2017-05-09	3691014	49.6 ppb
2017-08-08	3751651	108.7 ppb
2017-08-08	3751652	68.6 ppb
2017-08-08	3751653	63.3 ppb
2017-08-08	3751654	83.6 ppb
2017-08-08	3751655	73.9 ppb
2017-08-08	3751656	83.5 ppb
2017-08-08	3751657	71.0 ppb
2017-08-08	3751658	86.2 ppb
2017-11-16	3823064	41.2 ppb
2017-11-16	3823065	37.1 ppb
2017-11-16	3823066	35.8 ppb
2017-11-16	3823067	26.2 ppb
2017-11-16	3823068	27.5 ppb
2017-11-16	3823069	39.4 ppb
2017-11-16	3823070	58.5 ppb
2017-11-16	3823071	53.0 ppb
2018-02-13	3871444	29.6 ppb
2018-02-13	3871445	34.9 ppb
2018-02-13	3871446	36.3 ppb
2018-02-13	3871447	20.8 ppb
2018-02-13	3871448	15.3 ppb
2018-02-13	3871449	35.1 ppb
2018-02-13	3871450	26.2 ppb
2018-02-13	3871451	46.5 ppb
2018-05-08	3931391	46.8 ppb
2018-05-08	3931392	61.5 ppb
2018-05-08	3931393	63.0 ppb
2018-05-08	3931394	42.3 ppb
2018-05-08	3931395	29.3 ppb
2018-05-08	3931396	66.4 ppb
2018-05-08	3931397	45.1 ppb
2018-05-08	3931398	78.0 ppb
2018-05-24	3946294	69.6 ppb
2018-08-21	4031486	87.2 ppb
2018-08-21	4031487	56.3 ppb
2018-08-21	4031488	54.2 ppb
2018-08-21	4031489	75.4 ppb
2018-08-21	4031490	62.5 ppb
2018-08-21	4031491	60.3 ppb
2018-08-21	4031492	73.7 ppb
2018-08-21	4031493	94.8 ppb
2018-11-13	4121274	45.5 ppb
2018-11-13	4121276	54.1 ppb
2018-11-13	4121278	59.0 ppb
2018-11-13	4121353	48.4 ppb
2018-11-13	4121355	45.3 ppb
2018-11-13	4121357	42.8 ppb
2018-11-13	4121359	30.9 ppb
2018-11-13	4121361	43.9 ppb
2019-02-12	4195480-1	25.0 ppb
2019-02-12	4195481-1	29.0 ppb
2019-02-12	4195482-1	28.0 ppb
2019-02-12	4195483-1	18.0 ppb
2019-02-12	4195484-1	16.0 ppb
2019-02-12	4195485-1	29.0 ppb
2019-02-12	4195486-1	25.0 ppb
2019-02-12	4195487-1	35.0 ppb
2019-05-14	4294422	33.0 ppb
2019-05-14	4294424	46.0 ppb
2019-05-14	4294426	47.0 ppb
2019-05-14	4294428	35.0 ppb
2019-05-14	4294430	26.0 ppb
2019-05-14	4294432	50.0 ppb
2019-05-14	4294434	32.0 ppb
2019-05-14	4294436	50.0 ppb
2019-08-13	4385972	68.0 ppb
2019-08-13	4385974	60.0 ppb
2019-08-13	4385976	63.0 ppb
2019-08-13	4385978	63.0 ppb
2019-08-13	4385980	43.0 ppb
2019-08-13	4385982	68.0 ppb
2019-08-13	4385984	60.0 ppb
2019-08-13	4385986	77.0 ppb
2019-11-12	4483517	50.0 ppb
2019-11-12	4483519	53.0 ppb
2019-11-12	4483521	53.0 ppb
2019-11-12	4483523	36.0 ppb
2019-11-12	4483525	28.0 ppb
2019-11-12	4483527	61.0 ppb
2019-11-12	4483529	46.0 ppb
2019-11-12	4483531	62.0 ppb