Total trihalomethanes (TTHMs)

City of Santa Clara

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

213

Samples

Samples exceeding legal limit (MCL)

166

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	26.4 ppb	37	26	ND - 84.0 ppb
2015	25.8 ppb	40	24	ND - 73.0 ppb
2016	43.0 ppb	40	34	ND - 89.0 ppb
2017	29.2 ppb	32	28	ND - 52.0 ppb
2018	29.6 ppb	32	28	ND - 50.0 ppb
2019	26.6 ppb	32	26	ND - 64.0 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
2014-01-22	9590-900-1044	35.0 ppb
2014-01-22	9590-901-1030	28.0 ppb
2014-01-22	9590-902-1105	36.0 ppb
2014-01-22	9590-903-1015	2.20 ppb
2014-01-22	9590-904-0935	ND
2014-01-22	9590-905-0834	22.0 ppb
2014-01-22	9590-906-0854	45.0 ppb
2014-01-22	9590-907-0955	30.0 ppb
2014-04-02	9590-030-1035	ND
2014-04-23	9590-900-1025	30.0 ppb
2014-04-23	9590-901-1010	30.0 ppb
2014-04-23	9590-902-1040	32.0 ppb
2014-04-23	9590-903-0955	8.30 ppb
2014-04-23	9590-904-0910	14.0 ppb
2014-04-23	9590-905-0835	84.0 ppb
2014-04-23	9590-906-0850	71.0 ppb
2014-04-23	9590-907-0930	ND
2014-07-23	9590-900-1340	32.0 ppb
2014-07-23	9590-901-0905	ND
2014-07-23	9590-902-0945	33.0 ppb
2014-07-23	9590-903-0845	ND
2014-07-23	9590-904-1005	ND
2014-07-23	9590-905-1025	ND
2014-07-23	9590-906-1045	56.0 ppb
2014-07-23	9590-907-1130	58.0 ppb
2014-08-26	9590-027-1050	ND
2014-08-26	9590-034-0930	ND
2014-08-27	9590-011-0905	ND
2014-08-27	9590-036-1030	ND
2014-10-24	9590-900-0910	36.0 ppb
2014-10-24	9590-901-0930	38.0 ppb
2014-10-24	9590-902-0855	42.0 ppb
2014-10-24	9590-903-0915	10.00 ppb
2014-10-24	9590-904-1025	35.0 ppb
2014-10-24	9590-905-0935	60.0 ppb
2014-10-24	9590-906-0955	57.0 ppb
2014-10-24	9590-907-1045	52.0 ppb
2015-01-21	9590-900-1215	36.0 ppb
2015-01-21	9590-901-1142	41.0 ppb
2015-01-21	9590-902-1126	40.0 ppb
2015-01-21	9590-903-1150	ND
2015-01-21	9590-904-0948	3.70 ppb
2015-01-21	9590-905-1003	ND
2015-01-21	9590-906-1026	66.0 ppb
2015-01-21	9590-907-0926	30.0 ppb
2015-04-22	9590-900-0945	33.0 ppb
2015-04-22	9590-901-0915	33.0 ppb
2015-04-22	9590-902-1010	33.0 ppb
2015-04-22	9590-903-0858	ND
2015-04-22	9590-904-1125	20.0 ppb
2015-04-22	9590-905-1410	ND
2015-04-22	9590-906-1435	65.0 ppb
2015-04-22	9590-907-1140	ND
2015-07-23	9590-900-1410	33.0 ppb
2015-07-23	9590-901-1115	7.30 ppb
2015-07-23	9590-902-1345	31.0 ppb
2015-07-23	9590-903-1050	ND
2015-07-23	9590-904-0950	73.0 ppb
2015-07-23	9590-905-0850	71.0 ppb
2015-07-23	9590-906-0910	69.0 ppb
2015-07-23	9590-907-1015	43.0 ppb
2015-08-17	9590-004-0925	ND
2015-08-17	9590-019-1045	ND
2015-08-19	9590-002-0955	ND
2015-08-19	9590-015-1100	ND
2015-08-20	9590-007-1120	ND
2015-08-20	9590-031-1010	ND
2015-08-24	9590-013-0950	ND
2015-08-24	9590-014-1045	ND
2015-10-21	9590-900-1321	56.0 ppb
2015-10-21	9590-901-1125	14.0 ppb
2015-10-21	9590-902-1340	55.0 ppb
2015-10-21	9590-903-1108	ND
2015-10-21	9590-904-1022	54.0 ppb
2015-10-21	9590-905-0923	ND
2015-10-21	9590-906-0957	63.0 ppb
2015-10-21	9590-907-1041	63.0 ppb
2016-01-20	9590-900-1000	63.0 ppb
2016-01-20	9590-901-0935	41.0 ppb
2016-01-20	9590-902-1020	61.0 ppb
2016-01-20	9590-903-0915	4.50 ppb
2016-01-20	9590-904-1356	39.0 ppb
2016-01-20	9590-905-1045	75.0 ppb
2016-01-20	9590-906-1102	89.0 ppb
2016-01-20	9590-907-1413	77.0 ppb
2016-01-27	9590-900-1127	75.0 ppb
2016-01-27	9590-901-1105	72.0 ppb
2016-01-27	9590-902-1146	75.0 ppb
2016-01-27	9590-903-1050	64.0 ppb
2016-01-27	9590-904-1206	ND
2016-01-27	9590-905-1218	ND
2016-01-27	9590-906-1232	69.0 ppb
2016-01-27	9590-907-1356	74.0 ppb
2016-04-20	9590-900-1021	43.0 ppb
2016-04-20	9590-901-1002	31.0 ppb
2016-04-20	9590-902-1043	42.0 ppb
2016-04-20	9590-903-0942	ND
2016-04-20	9590-904-1159	ND
2016-04-20	9590-905-1106	ND
2016-04-20	9590-906-1129	56.0 ppb
2016-04-20	9590-907-1224	53.0 ppb
2016-07-20	9590-900-1103	54.0 ppb
2016-07-20	9590-901-0827	53.0 ppb
2016-07-20	9590-902-0855	57.0 ppb
2016-07-20	9590-903-0809	20.0 ppb
2016-07-20	9590-904-1007	34.0 ppb
2016-07-20	9590-905-0925	46.0 ppb
2016-07-20	9590-906-0942	46.0 ppb
2016-07-20	9590-907-1022	ND
2016-10-26	9590-900-0927	48.0 ppb
2016-10-26	9590-901-0914	47.0 ppb
2016-10-26	9590-902-0940	47.0 ppb
2016-10-26	9590-903-0901	1.60 ppb
2016-10-26	9590-904-1055	50.0 ppb
2016-10-26	9590-905-1003	17.0 ppb
2016-10-26	9590-906-1021	48.0 ppb
2016-10-26	9590-907-1108	49.0 ppb
2017-01-25	9590-900-1128	18.0 ppb
2017-01-25	9590-901-1201	20.0 ppb
2017-01-25	9590-902-1054	22.0 ppb
2017-01-25	9590-903-1146	19.0 ppb
2017-01-25	9590-904-0959	ND
2017-01-25	9590-905-0852	25.0 ppb
2017-01-25	9590-906-0915	51.0 ppb
2017-01-25	9590-907-1028	29.0 ppb
2017-04-19	9590-900-1200	45.0 ppb
2017-04-19	9590-901-1048	46.0 ppb
2017-04-19	9590-902-1219	47.0 ppb
2017-04-19	9590-903-1035	47.0 ppb
2017-04-19	9590-904-0952	ND
2017-04-19	9590-905-0838	14.0 ppb
2017-04-19	9590-906-0903	45.0 ppb
2017-04-19	9590-907-1010	52.0 ppb
2017-08-02	9590-900-1053	38.0 ppb
2017-08-02	9590-901-1038	42.0 ppb
2017-08-02	9590-902-1118	41.0 ppb
2017-08-02	9590-903-1025	ND
2017-08-02	9590-904-0938	30.0 ppb
2017-08-02	9590-905-0841	35.0 ppb
2017-08-02	9590-906-0901	31.0 ppb
2017-08-02	9590-907-0953	ND
2017-10-18	9590-900-1014	36.0 ppb
2017-10-18	9590-901-0929	36.0 ppb
2017-10-18	9590-902-0959	36.0 ppb
2017-10-18	9590-903-0914	30.0 ppb
2017-10-18	9590-904-1144	26.0 ppb
2017-10-18	9590-905-1155	29.0 ppb
2017-10-18	9590-906-1253	28.0 ppb
2017-10-18	9590-907-1212	17.0 ppb
2018-01-29	9590-900-0755	30.0 ppb
2018-01-29	9590-901-0843	28.0 ppb
2018-01-29	9590-902-0817	32.0 ppb
2018-01-29	9590-903-0832	21.0 ppb
2018-01-29	9590-904-1008	ND
2018-01-29	9590-905-0909	19.0 ppb
2018-01-29	9590-906-0928	46.0 ppb
2018-01-29	9590-907-1023	50.0 ppb
2018-05-23	9590-900-1004	46.0 ppb
2018-05-25	9590-901-0947	43.0 ppb
2018-05-25	9590-902-1025	18.0 ppb
2018-05-25	9590-903-0939	40.0 ppb
2018-05-25	9590-904-0608	25.0 ppb
2018-05-25	9590-905-0818	36.0 ppb
2018-05-25	9590-906-0835	34.0 ppb
2018-05-25	9590-907-0913	ND
2018-07-25	9590-900-0900	41.0 ppb
2018-07-25	9590-901-0848	40.0 ppb
2018-07-25	9590-902-0915	13.0 ppb
2018-07-25	9590-903-0838	40.0 ppb
2018-07-25	9590-904-1015	35.0 ppb
2018-07-25	9590-905-0939	ND
2018-07-25	9590-906-0954	36.0 ppb
2018-07-25	9590-907-1027	32.0 ppb
2018-10-17	9590-900-0930	34.0 ppb
2018-10-17	9590-901-0904	34.0 ppb
2018-10-17	9590-902-0946	32.0 ppb
2018-10-17	9590-903-0850	20.0 ppb
2018-10-17	9590-904-1007	39.0 ppb
2018-10-17	9590-905-1019	42.0 ppb
2018-10-17	9590-906-1054	42.0 ppb
2018-10-17	9590-907-1117	ND
2019-01-16	9590-900-0957	16.0 ppb
2019-01-16	9590-901-0934	15.0 ppb
2019-01-16	9590-902-1016	8.20 ppb
2019-01-16	9590-903-0924	15.0 ppb
2019-01-16	9590-904-0741	41.0 ppb
2019-01-16	9590-905-0753	64.0 ppb
2019-01-16	9590-906-0809	58.0 ppb
2019-01-16	9590-907-0852	ND
2019-04-17	9590-900-0934	32.0 ppb
2019-04-17	9590-901-0918	33.0 ppb
2019-04-17	9590-902-0949	14.0 ppb
2019-04-17	9590-903-0906	33.0 ppb
2019-04-17	9590-904-1012	6.60 ppb
2019-04-17	9590-905-1028	ND
2019-04-17	9590-906-1055	40.0 ppb
2019-04-17	9590-907-1119	45.0 ppb
2019-07-15	9590-900-1116	45.0 ppb
2019-07-15	9590-901-1056	44.0 ppb
2019-07-15	9590-902-1129	42.0 ppb
2019-07-15	9590-903-1040	ND
2019-07-15	9590-904-0949	41.0 ppb
2019-07-15	9590-905-1009	42.0 ppb
2019-07-15	9590-906-0926	41.0 ppb
2019-07-15	9590-907-0843	ND
2019-10-15	9590-900-0814	39.0 ppb
2019-10-15	9590-901-0758	40.0 ppb
2019-10-15	9590-902-0834	45.0 ppb
2019-10-15	9590-903-0745	1.70 ppb
2019-10-15	9590-904-1017	17.0 ppb
2019-10-15	9590-905-0941	ND
2019-10-15	9590-906-0958	32.0 ppb
2019-10-15	9590-907-1028	ND