Total trihalomethanes (TTHMs)

Falmouth 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

357

Samples

Samples exceeding legal limit (MCL)

349

Samples exceeding
health guidelines

Testing results - average by year

Year	Average result	Samples taken	Detections	Range of results
2013	N/A	0	0	N/A
2014	4.32 ppb	4	4	0.780 ppb - 13.8 ppb
2015	34.3 ppb	69	69	0.730 ppb - 93.0 ppb
2016	31.6 ppb	78	75	ND - 97.6 ppb
2017	27.7 ppb	68	67	ND - 83.0 ppb
2018	13.6 ppb	70	66	ND - 33.4 ppb
2019	14.7 ppb	68	68	1.38 ppb - 31.6 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	Result
2014-01-14	13.8 ppb
2014-04-03	0.780 ppb
2014-07-10	1.77 ppb
2014-10-08	0.940 ppb
2015-01-13	6.45 ppb
2015-03-12	4.10 ppb
2015-03-12	4.10 ppb
2015-03-12	7.47 ppb
2015-03-12	7.47 ppb
2015-03-12	79.9 ppb
2015-03-12	79.9 ppb
2015-03-12	76.5 ppb
2015-03-12	76.5 ppb
2015-03-12	27.5 ppb
2015-03-12	27.5 ppb
2015-03-12	5.32 ppb
2015-03-12	5.32 ppb
2015-03-12	6.10 ppb
2015-03-12	6.10 ppb
2015-03-12	34.4 ppb
2015-03-12	34.4 ppb
2015-04-02	0.820 ppb
2015-06-04	6.25 ppb
2015-06-04	6.25 ppb
2015-06-04	27.0 ppb
2015-06-04	27.0 ppb
2015-06-04	72.2 ppb
2015-06-04	72.2 ppb
2015-06-04	67.3 ppb
2015-06-04	67.3 ppb
2015-06-04	19.9 ppb
2015-06-04	19.9 ppb
2015-06-04	21.3 ppb
2015-06-04	21.3 ppb
2015-06-04	25.0 ppb
2015-06-04	25.0 ppb
2015-06-04	21.5 ppb
2015-06-04	21.5 ppb
2015-07-07	0.890 ppb
2015-08-20	1.02 ppb
2015-09-03	8.14 ppb
2015-09-03	8.14 ppb
2015-09-03	44.8 ppb
2015-09-03	44.8 ppb
2015-09-03	78.9 ppb
2015-09-03	78.9 ppb
2015-09-03	63.1 ppb
2015-09-03	63.1 ppb
2015-09-03	38.4 ppb
2015-09-03	38.4 ppb
2015-09-03	23.6 ppb
2015-09-03	23.6 ppb
2015-09-03	46.9 ppb
2015-09-03	46.9 ppb
2015-09-03	30.4 ppb
2015-09-03	30.4 ppb
2015-10-15	0.730 ppb
2015-12-03	7.86 ppb
2015-12-03	7.86 ppb
2015-12-03	26.8 ppb
2015-12-03	26.8 ppb
2015-12-03	91.9 ppb
2015-12-03	91.9 ppb
2015-12-03	93.0 ppb
2015-12-03	93.0 ppb
2015-12-03	45.3 ppb
2015-12-03	45.3 ppb
2015-12-03	18.3 ppb
2015-12-03	18.3 ppb
2015-12-03	5.50 ppb
2015-12-03	5.50 ppb
2015-12-03	52.9 ppb
2015-12-03	52.9 ppb
2016-01-11	9.65 ppb
2016-01-12	ND
2016-01-26	ND
2016-01-27	7.44 ppb
2016-01-28	13.8 ppb
2016-02-04	16.0 ppb
2016-02-05	15.5 ppb
2016-02-08	18.3 ppb
2016-02-09	13.2 ppb
2016-02-10	31.5 ppb
2016-03-02	2.97 ppb
2016-03-02	2.97 ppb
2016-03-02	15.1 ppb
2016-03-02	15.1 ppb
2016-03-02	90.9 ppb
2016-03-02	90.9 ppb
2016-03-02	55.7 ppb
2016-03-02	55.7 ppb
2016-03-02	36.0 ppb
2016-03-02	36.0 ppb
2016-03-02	23.6 ppb
2016-03-02	23.6 ppb
2016-03-02	10.7 ppb
2016-03-02	10.7 ppb
2016-03-02	36.8 ppb
2016-03-02	36.8 ppb
2016-04-11	3.02 ppb
2016-05-20	ND
2016-06-02	7.33 ppb
2016-06-02	7.33 ppb
2016-06-02	26.0 ppb
2016-06-02	26.0 ppb
2016-06-02	71.6 ppb
2016-06-02	71.6 ppb
2016-06-02	47.8 ppb
2016-06-02	47.8 ppb
2016-06-02	25.9 ppb
2016-06-02	25.9 ppb
2016-06-02	25.8 ppb
2016-06-02	25.8 ppb
2016-06-02	30.1 ppb
2016-06-02	30.1 ppb
2016-06-02	25.1 ppb
2016-06-02	25.1 ppb
2016-07-18	0.840 ppb
2016-09-01	20.7 ppb
2016-09-01	20.7 ppb
2016-09-01	60.6 ppb
2016-09-01	60.6 ppb
2016-09-01	77.0 ppb
2016-09-01	77.0 ppb
2016-09-01	67.6 ppb
2016-09-01	67.6 ppb
2016-09-01	45.6 ppb
2016-09-01	45.6 ppb
2016-09-01	27.1 ppb
2016-09-01	27.1 ppb
2016-09-01	97.6 ppb
2016-09-01	97.6 ppb
2016-09-01	30.9 ppb
2016-09-01	30.9 ppb
2016-10-04	0.760 ppb
2016-12-05	6.64 ppb
2016-12-05	6.64 ppb
2016-12-05	15.8 ppb
2016-12-05	15.8 ppb
2016-12-05	57.8 ppb
2016-12-05	57.8 ppb
2016-12-05	31.0 ppb
2016-12-05	31.0 ppb
2016-12-05	39.8 ppb
2016-12-05	39.8 ppb
2016-12-05	15.1 ppb
2016-12-05	15.1 ppb
2016-12-05	11.6 ppb
2016-12-05	11.6 ppb
2016-12-05	32.1 ppb
2016-12-05	32.1 ppb
2017-01-04	4.38 ppb
2017-03-06	7.41 ppb
2017-03-06	7.41 ppb
2017-03-06	16.1 ppb
2017-03-06	16.1 ppb
2017-03-06	48.8 ppb
2017-03-06	48.8 ppb
2017-03-06	49.9 ppb
2017-03-06	49.9 ppb
2017-03-06	21.4 ppb
2017-03-06	21.4 ppb
2017-03-06	9.34 ppb
2017-03-06	9.34 ppb
2017-03-06	13.7 ppb
2017-03-06	13.7 ppb
2017-03-06	22.7 ppb
2017-03-06	22.7 ppb
2017-04-06	1.44 ppb
2017-05-12	7.14 ppb
2017-06-05	28.9 ppb
2017-06-05	28.9 ppb
2017-06-05	16.4 ppb
2017-06-05	16.4 ppb
2017-06-05	83.0 ppb
2017-06-05	83.0 ppb
2017-06-05	52.0 ppb
2017-06-05	52.0 ppb
2017-06-05	42.6 ppb
2017-06-05	42.6 ppb
2017-06-05	32.0 ppb
2017-06-05	32.0 ppb
2017-06-05	42.3 ppb
2017-06-05	42.3 ppb
2017-06-05	26.3 ppb
2017-06-05	26.3 ppb
2017-09-05	19.5 ppb
2017-09-05	19.5 ppb
2017-09-05	39.7 ppb
2017-09-05	39.7 ppb
2017-09-05	63.9 ppb
2017-09-05	63.9 ppb
2017-09-05	43.8 ppb
2017-09-05	43.8 ppb
2017-09-05	29.7 ppb
2017-09-05	29.7 ppb
2017-09-05	22.1 ppb
2017-09-05	22.1 ppb
2017-09-05	40.4 ppb
2017-09-05	40.4 ppb
2017-09-05	27.4 ppb
2017-09-05	27.4 ppb
2017-10-24	ND
2017-12-04	8.26 ppb
2017-12-04	8.26 ppb
2017-12-04	8.19 ppb
2017-12-04	8.19 ppb
2017-12-04	26.2 ppb
2017-12-04	26.2 ppb
2017-12-04	31.5 ppb
2017-12-04	31.5 ppb
2017-12-04	22.7 ppb
2017-12-04	22.7 ppb
2017-12-04	3.71 ppb
2017-12-04	3.71 ppb
2017-12-04	6.54 ppb
2017-12-04	6.54 ppb
2017-12-04	30.4 ppb
2017-12-04	30.4 ppb
2018-01-08	ND
2018-03-05	4.77 ppb
2018-03-05	4.77 ppb
2018-03-05	5.83 ppb
2018-03-05	5.83 ppb
2018-03-05	15.2 ppb
2018-03-05	15.2 ppb
2018-03-05	23.0 ppb
2018-03-05	23.0 ppb
2018-03-05	9.24 ppb
2018-03-05	9.24 ppb
2018-03-05	ND
2018-03-05	ND
2018-03-05	1.12 ppb
2018-03-05	1.12 ppb
2018-03-05	21.6 ppb
2018-03-05	21.6 ppb
2018-04-10	0.330 ppb
2018-04-17	ND
2018-06-04	9.53 ppb
2018-06-04	9.53 ppb
2018-06-04	13.0 ppb
2018-06-04	13.0 ppb
2018-06-04	23.9 ppb
2018-06-04	23.9 ppb
2018-06-04	9.84 ppb
2018-06-04	9.84 ppb
2018-06-04	9.74 ppb
2018-06-04	9.74 ppb
2018-06-04	6.15 ppb
2018-06-04	6.15 ppb
2018-06-04	4.10 ppb
2018-06-04	4.10 ppb
2018-06-04	16.6 ppb
2018-06-04	16.6 ppb
2018-07-17	1.56 ppb
2018-09-05	18.0 ppb
2018-09-05	18.0 ppb
2018-09-05	28.8 ppb
2018-09-05	28.8 ppb
2018-09-05	22.8 ppb
2018-09-05	22.8 ppb
2018-09-05	20.8 ppb
2018-09-05	20.8 ppb
2018-09-05	7.37 ppb
2018-09-05	7.37 ppb
2018-09-05	16.0 ppb
2018-09-05	16.0 ppb
2018-09-05	19.1 ppb
2018-09-05	19.1 ppb
2018-09-06	32.6 ppb
2018-09-06	32.6 ppb
2018-10-02	3.48 ppb
2018-10-09	0.670 ppb
2018-12-07	5.92 ppb
2018-12-07	5.92 ppb
2018-12-07	14.0 ppb
2018-12-07	14.0 ppb
2018-12-07	23.9 ppb
2018-12-07	23.9 ppb
2018-12-07	25.8 ppb
2018-12-07	25.8 ppb
2018-12-07	18.4 ppb
2018-12-07	18.4 ppb
2018-12-07	2.43 ppb
2018-12-07	2.43 ppb
2018-12-07	11.0 ppb
2018-12-07	11.0 ppb
2018-12-07	33.4 ppb
2018-12-07	33.4 ppb
2019-01-08	1.38 ppb
2019-03-18	5.27 ppb
2019-03-18	5.27 ppb
2019-03-18	6.09 ppb
2019-03-18	6.09 ppb
2019-03-18	22.1 ppb
2019-03-18	22.1 ppb
2019-03-18	20.1 ppb
2019-03-18	20.1 ppb
2019-03-18	18.7 ppb
2019-03-18	18.7 ppb
2019-03-18	1.98 ppb
2019-03-18	1.98 ppb
2019-03-18	5.07 ppb
2019-03-18	5.07 ppb
2019-03-18	24.0 ppb
2019-03-18	24.0 ppb
2019-05-15	4.36 ppb
2019-06-12	8.51 ppb
2019-06-12	8.51 ppb
2019-06-12	13.8 ppb
2019-06-12	13.8 ppb
2019-06-12	22.8 ppb
2019-06-12	22.8 ppb
2019-06-12	19.9 ppb
2019-06-12	19.9 ppb
2019-06-12	18.3 ppb
2019-06-12	18.3 ppb
2019-06-12	6.80 ppb
2019-06-12	6.80 ppb
2019-06-12	9.63 ppb
2019-06-12	9.63 ppb
2019-06-12	19.0 ppb
2019-06-12	19.0 ppb
2019-07-09	6.53 ppb
2019-09-12	20.3 ppb
2019-09-12	20.3 ppb
2019-09-12	15.3 ppb
2019-09-12	15.3 ppb
2019-09-12	18.9 ppb
2019-09-12	18.9 ppb
2019-09-12	19.6 ppb
2019-09-12	19.6 ppb
2019-09-12	16.4 ppb
2019-09-12	16.4 ppb
2019-09-12	6.51 ppb
2019-09-12	6.51 ppb
2019-09-12	19.6 ppb
2019-09-12	19.6 ppb
2019-09-12	21.4 ppb
2019-09-12	21.4 ppb
2019-10-01	3.21 ppb
2019-12-09	10.1 ppb
2019-12-09	10.1 ppb
2019-12-09	10.7 ppb
2019-12-09	10.7 ppb
2019-12-09	23.6 ppb
2019-12-09	23.6 ppb
2019-12-09	31.6 ppb
2019-12-09	31.6 ppb
2019-12-09	21.6 ppb
2019-12-09	21.6 ppb
2019-12-09	1.97 ppb
2019-12-09	1.97 ppb
2019-12-09	3.43 ppb
2019-12-09	3.43 ppb
2019-12-09	29.7 ppb
2019-12-09	29.7 ppb