Total trihalomethanes (TTHMs)

California Water Service (CWS) - Bakersfield

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

189

Samples

Samples exceeding legal limit (MCL)

174

Samples exceeding
health guidelines

Testing results - average by year

Year	Average result	Samples taken	Detections	Range of results
2014	18.7 ppb	28	26	ND - 85.2 ppb
2015	28.4 ppb	32	30	ND - 92.5 ppb
2016	44.7 ppb	32	28	ND - 74.1 ppb
2017	38.5 ppb	33	30	ND - 71.8 ppb
2018	43.5 ppb	32	30	ND - 75.0 ppb
2019	43.3 ppb	32	30	ND - 78.4 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
2014-01-21	5701-900-1010	12.2 ppb
2014-01-21	5701-904-1030	12.5 ppb
2014-01-21	5701-905-0928	ND
2014-01-21	5701-906-0954	8.40 ppb
2014-04-21	5701-901-1410	74.7 ppb
2014-04-21	5701-902-1437	52.7 ppb
2014-04-21	5701-903-1502	2.70 ppb
2014-04-21	5701-904-1615	47.6 ppb
2014-04-21	5701-907-1450	3.50 ppb
2014-04-22	5701-900-1650	25.6 ppb
2014-04-22	5701-905-1540	0.700 ppb
2014-04-22	5701-906-1710	41.3 ppb
2014-07-23	5701-900-1047	10.7 ppb
2014-07-23	5701-901-1307	57.0 ppb
2014-07-23	5701-902-1232	11.8 ppb
2014-07-23	5701-903-1107	2.30 ppb
2014-07-23	5701-904-1137	10.5 ppb
2014-07-23	5701-905-0937	0.600 ppb
2014-07-23	5701-906-1022	12.4 ppb
2014-07-23	5701-907-1122	4.90 ppb
2014-10-23	5701-900-1130	11.2 ppb
2014-10-23	5701-901-1240	85.2 ppb
2014-10-23	5701-902-1145	17.0 ppb
2014-10-23	5701-903-1040	0.900 ppb
2014-10-23	5701-904-1205	10.6 ppb
2014-10-23	5701-905-1020	ND
2014-10-23	5701-906-1115	3.20 ppb
2014-10-23	5701-907-1055	3.20 ppb
2015-01-21	5701-900-0834	33.2 ppb
2015-01-21	5701-901-0832	53.4 ppb
2015-01-21	5701-902-0834	42.0 ppb
2015-01-21	5701-903-0834	4.20 ppb
2015-01-21	5701-904-0832	17.6 ppb
2015-01-21	5701-905-0832	0.600 ppb
2015-01-21	5701-906-0832	12.3 ppb
2015-01-21	5701-907-0834	40.1 ppb
2015-04-27	5701-900-0919	25.7 ppb
2015-04-27	5701-901-0919	51.4 ppb
2015-04-27	5701-902-0919	30.8 ppb
2015-04-27	5701-903-0919	1.90 ppb
2015-04-27	5701-904-0919	51.9 ppb
2015-04-27	5701-905-0919	ND
2015-04-27	5701-906-0919	14.2 ppb
2015-04-27	5701-907-0919	17.0 ppb
2015-07-22	5701-900-0856	26.0 ppb
2015-07-22	5701-901-0856	92.5 ppb
2015-07-22	5701-902-0856	13.9 ppb
2015-07-22	5701-903-0856	11.2 ppb
2015-07-22	5701-904-0856	11.7 ppb
2015-07-22	5701-905-0856	ND
2015-07-22	5701-906-0856	14.2 ppb
2015-07-22	5701-907-0856	16.3 ppb
2015-10-19	5701-900-0910	16.3 ppb
2015-10-19	5701-901-0910	78.2 ppb
2015-10-19	5701-902-0910	70.7 ppb
2015-10-19	5701-903-0910	30.5 ppb
2015-10-19	5701-904-0910	72.4 ppb
2015-10-19	5701-905-0910	0.900 ppb
2015-10-19	5701-906-0910	16.2 ppb
2015-10-19	5701-907-0910	43.0 ppb
2016-01-20	5701-900-0848	ND
2016-01-20	5810-901-1015	69.0 ppb
2016-01-20	5810-902-0945	54.0 ppb
2016-01-20	5810-903-0900	43.0 ppb
2016-01-20	5701-904-0848	63.1 ppb
2016-01-20	5701-905-0848	37.4 ppb
2016-01-20	5701-906-0848	21.1 ppb
2016-01-20	5810-907-0920	47.0 ppb
2016-04-18	5701-900-0832	55.8 ppb
2016-04-18	5701-901-0832	74.1 ppb
2016-04-18	5701-902-0832	62.5 ppb
2016-04-18	5701-903-0832	55.3 ppb
2016-04-18	5701-904-0832	50.9 ppb
2016-04-18	5701-905-0832	ND
2016-04-18	5701-906-0832	48.6 ppb
2016-04-18	5701-907-0832	35.6 ppb
2016-07-18	5701-900-0826	52.2 ppb
2016-07-18	5701-901-0823	64.9 ppb
2016-07-18	5701-902-0826	50.2 ppb
2016-07-18	5701-903-0823	20.7 ppb
2016-07-18	5701-904-0823	45.6 ppb
2016-07-18	5701-905-0826	ND
2016-07-18	5701-906-0826	48.0 ppb
2016-07-18	5701-907-0823	60.4 ppb
2016-10-18	5701-900-0919	67.4 ppb
2016-10-18	5701-901-0919	67.7 ppb
2016-10-18	5701-902-0919	61.8 ppb
2016-10-18	5701-903-0919	45.6 ppb
2016-10-18	5701-904-0919	44.1 ppb
2016-10-18	5701-905-0919	ND
2016-10-18	5701-906-0919	34.6 ppb
2016-10-18	5701-907-0919	49.4 ppb
2017-01-17	5701-900-0830	55.3 ppb
2017-01-17	5701-901-0830	71.8 ppb
2017-01-17	5701-902-0830	54.3 ppb
2017-01-17	5701-903-0830	11.8 ppb
2017-01-17	5701-904-0830	23.9 ppb
2017-01-17	5701-905-0830	0.800 ppb
2017-01-17	5701-906-0830	23.4 ppb
2017-01-17	5701-907-0830	41.9 ppb
2017-04-17	5810-900-1326	71.0 ppb
2017-04-17	5810-901-1445	71.0 ppb
2017-04-17	5810-902-1354	67.0 ppb
2017-04-17	5810-903-1422	44.0 ppb
2017-04-17	5810-904-1344	64.0 ppb
2017-04-17	5810-905-1249	ND
2017-04-17	5810-906-1313	60.0 ppb
2017-04-17	5810-907-1409	67.0 ppb
2017-07-17	5810-900-1408	42.0 ppb
2017-07-17	5810-901-1338	27.0 ppb
2017-07-17	5810-902-1251	38.0 ppb
2017-07-17	5810-903-1445	15.0 ppb
2017-07-17	5810-904-1433	37.0 ppb
2017-07-17	5810-905-1326	ND
2017-07-17	5810-906-1351	42.0 ppb
2017-07-17	5810-907-1309	24.0 ppb
2017-08-02	9590-904-0935	42.0 ppb
2017-10-16	5810-900-1114	50.0 ppb
2017-10-16	5810-901-1428	68.0 ppb
2017-10-16	5810-902-1249	44.0 ppb
2017-10-16	5810-903-1345	17.0 ppb
2017-10-16	5810-904-1141	34.0 ppb
2017-10-16	5810-905-0945	ND
2017-10-16	5810-906-1042	38.0 ppb
2017-10-16	5810-907-1315	25.0 ppb
2018-01-18	5810-900-1045	46.0 ppb
2018-01-18	5810-901-1230	75.0 ppb
2018-01-18	5810-902-1105	54.0 ppb
2018-01-18	5810-903-1310	28.0 ppb
2018-01-18	5810-904-1115	64.0 ppb
2018-01-18	5810-905-0945	42.0 ppb
2018-01-18	5810-906-1030	27.0 ppb
2018-01-18	5810-907-1255	61.0 ppb
2018-04-16	5701-900-1406	54.5 ppb
2018-04-16	5701-901-1406	63.3 ppb
2018-04-16	5701-902-1406	55.8 ppb
2018-04-16	5701-903-1406	46.9 ppb
2018-04-16	5701-904-1406	57.4 ppb
2018-04-16	5701-905-1406	ND
2018-04-16	5701-906-1406	17.7 ppb
2018-04-16	5701-907-1406	62.3 ppb
2018-07-17	5701-900-0657	53.6 ppb
2018-07-17	5701-901-0657	55.2 ppb
2018-07-17	5701-902-0657	45.0 ppb
2018-07-17	5701-903-0657	23.7 ppb
2018-07-17	5701-904-0657	37.2 ppb
2018-07-17	5701-905-0657	ND
2018-07-17	5701-906-0657	41.9 ppb
2018-07-17	5701-907-0657	41.6 ppb
2018-10-16	5701-900-0719	38.9 ppb
2018-10-16	5701-901-0719	67.1 ppb
2018-10-16	5701-902-0719	36.2 ppb
2018-10-16	5701-903-0719	36.0 ppb
2018-10-16	5701-904-0719	33.9 ppb
2018-10-16	5701-905-0719	50.8 ppb
2018-10-16	5701-906-0719	35.6 ppb
2018-10-16	5701-907-0719	40.6 ppb
2019-01-14	5701-900-0831	73.8 ppb
2019-01-14	5701-901-0831	71.9 ppb
2019-01-14	5701-902-0831	74.5 ppb
2019-01-14	5701-903-0831	50.2 ppb
2019-01-14	5701-904-0831	63.7 ppb
2019-01-14	5701-905-0831	0.700 ppb
2019-01-14	5701-906-0831	42.7 ppb
2019-01-14	5701-907-0831	74.5 ppb
2019-04-15	5701-900-0936	52.8 ppb
2019-04-15	5701-901-0936	78.4 ppb
2019-04-15	5701-902-0936	68.2 ppb
2019-04-15	5701-903-0936	56.3 ppb
2019-04-15	5701-904-0936	47.2 ppb
2019-04-15	5701-905-0936	1.20 ppb
2019-04-15	5701-906-0936	47.5 ppb
2019-04-15	5701-907-0936	55.8 ppb
2019-07-16	5701-900-1020	46.1 ppb
2019-07-16	5701-901-1140	53.9 ppb
2019-07-16	5701-902-1035	39.0 ppb
2019-07-16	5701-903-1110	55.7 ppb
2019-07-16	5701-904-1005	33.9 ppb
2019-07-16	5701-905-0941	ND
2019-07-16	5701-906-1050	16.9 ppb
2019-07-16	5701-907-1100	40.2 ppb
2019-10-23	5701-900-1138	32.2 ppb
2019-10-23	5701-901-1114	42.3 ppb
2019-10-23	5701-902-1340	35.8 ppb
2019-10-23	5701-903-1040	43.0 ppb
2019-10-23	5701-904-1326	27.3 ppb
2019-10-23	5701-905-1435	ND
2019-10-23	5701-906-1302	15.6 ppb
2019-10-23	5701-907-1053	43.0 ppb