Total trihalomethanes (TTHMs)

City of La Habra

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

184

Samples

Samples exceeding legal limit (MCL)

149

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	13.8 ppb	24	20	ND - 42.5 ppb
2015	8.34 ppb	32	29	ND - 37.4 ppb
2016	14.1 ppb	32	24	ND - 53.7 ppb
2017	9.27 ppb	32	20	ND - 33.3 ppb
2018	18.1 ppb	32	26	ND - 62.9 ppb
2019	28.5 ppb	32	30	ND - 126.1 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
2014-02-13	3761-801-1414	29.4 ppb
2014-02-13	3761-802-1328	14.8 ppb
2014-02-13	3761-803-1341	26.4 ppb
2014-02-13	3761-804-1425	28.5 ppb
2014-02-13	3761-805-1403	42.5 ppb
2014-02-13	3761-806-1441	6.00 ppb
2014-02-13	3761-807-1237	19.6 ppb
2014-02-13	3761-808-1520	32.6 ppb
2014-05-15	3761-801-1021	4.90 ppb
2014-05-15	3761-802-0954	ND
2014-05-15	3761-803-1000	ND
2014-05-15	3761-804-1029	4.60 ppb
2014-05-15	3761-805-1008	ND
2014-05-15	3761-806-0945	ND
2014-05-15	3761-807-0936	2.00 ppb
2014-05-15	3761-808-0926	8.10 ppb
2014-08-14	3761-801-1025	14.9 ppb
2014-08-14	3761-802-1059	16.5 ppb
2014-08-14	3761-803-1045	16.9 ppb
2014-08-14	3761-804-1034	12.5 ppb
2014-08-14	3761-805-1052	15.0 ppb
2014-08-14	3761-806-1005	9.40 ppb
2014-08-14	3761-807-1013	17.7 ppb
2014-08-14	3761-808-0955	9.40 ppb
2015-02-13	3761-801-1242	5.50 ppb
2015-02-13	3761-802-1220	2.70 ppb
2015-02-13	3761-803-1227	2.80 ppb
2015-02-13	3761-804-1250	5.40 ppb
2015-02-13	3761-805-1233	2.60 ppb
2015-02-13	3761-806-1303	1.30 ppb
2015-02-13	3761-807-1315	ND
2015-02-13	3761-808-1330	10.9 ppb
2015-05-14	3761-801-1230	6.70 ppb
2015-05-14	3761-802-1030	37.4 ppb
2015-05-14	3761-803-1115	6.40 ppb
2015-05-14	3761-804-1215	6.30 ppb
2015-05-14	3761-805-1130	28.7 ppb
2015-05-14	3761-806-1145	6.00 ppb
2015-05-14	3761-807-1045	14.8 ppb
2015-05-14	3761-808-1030	28.7 ppb
2015-08-14	3761-801-1150	2.90 ppb
2015-08-14	3761-802-1225	7.90 ppb
2015-08-14	3761-803-1240	4.10 ppb
2015-08-14	3761-804-1205	2.70 ppb
2015-08-14	3761-805-1305	10.3 ppb
2015-08-14	3761-806-1320	15.5 ppb
2015-08-14	3761-807-1135	ND
2015-08-14	3761-808-1120	ND
2015-11-09	3761-801-1354	4.40 ppb
2015-11-09	3761-802-1318	6.10 ppb
2015-11-09	3761-803-1329	3.70 ppb
2015-11-09	3761-804-1403	2.30 ppb
2015-11-09	3761-805-1344	5.60 ppb
2015-11-09	3761-806-1418	2.50 ppb
2015-11-09	3761-807-1250	20.8 ppb
2015-11-09	3761-808-1322	11.8 ppb
2016-02-08	3761-801-1236	9.10 ppb
2016-02-08	3761-802-1317	7.40 ppb
2016-02-08	3761-803-1312	7.80 ppb
2016-02-08	3761-804-1243	8.90 ppb
2016-02-08	3761-805-1256	11.0 ppb
2016-02-08	3761-806-1330	6.20 ppb
2016-02-08	3761-807-1339	15.0 ppb
2016-02-08	3761-808-1121	22.7 ppb
2016-05-09	3761-801-1425	26.9 ppb
2016-05-09	3761-802-1400	21.9 ppb
2016-05-09	3761-803-1415	29.1 ppb
2016-05-09	3761-804-1455	31.7 ppb
2016-05-09	3761-805-1430	53.7 ppb
2016-05-09	3761-806-1505	16.1 ppb
2016-05-09	3761-807-1300	41.5 ppb
2016-05-09	3761-808-1140	46.3 ppb
2016-08-08	3761-801-1353	15.0 ppb
2016-08-08	3761-802-1311	10.5 ppb
2016-08-08	3761-803-1320	12.2 ppb
2016-08-08	3761-804-1410	15.4 ppb
2016-08-08	3761-805-1329	ND
2016-08-08	3761-806-1419	18.2 ppb
2016-08-08	3761-807-1122	12.2 ppb
2016-08-08	3761-808-1220	6.20 ppb
2016-11-09	3761-801-1030	ND
2016-11-09	3761-802-1102	ND
2016-11-09	3761-803-1054	ND
2016-11-09	3761-804-1035	ND
2016-11-09	3761-805-1042	ND
2016-11-09	3761-806-1115	ND
2016-11-09	3761-807-1020	ND
2016-11-09	3761-808-1134	7.00 ppb
2017-02-13	3761-801-1326	ND
2017-02-13	3761-802-1148	ND
2017-02-13	3761-803-1302	ND
2017-02-13	3761-804-1336	ND
2017-02-13	3761-805-1315	ND
2017-02-13	3761-806-1357	ND
2017-02-13	3761-807-1213	ND
2017-02-13	3761-808-1105	23.9 ppb
2017-05-09	3761-801-1038	8.20 ppb
2017-05-09	3761-802-1112	6.80 ppb
2017-05-09	3761-803-1103	7.70 ppb
2017-05-09	3761-804-1047	8.70 ppb
2017-05-09	3761-805-1054	8.90 ppb
2017-05-09	3761-806-1022	8.00 ppb
2017-05-09	3761-807-1029	30.6 ppb
2017-05-09	3761-808-1010	33.3 ppb
2017-08-07	3761-801-1400	9.50 ppb
2017-08-07	3761-802-1310	19.6 ppb
2017-08-07	3761-803-1316	29.6 ppb
2017-08-07	3761-804-1413	13.7 ppb
2017-08-07	3761-805-1330	19.7 ppb
2017-08-07	3761-806-1428	13.8 ppb
2017-08-07	3761-807-1102	22.7 ppb
2017-08-07	3761-808-1151	19.5 ppb
2017-11-13	3761-801-1304	2.80 ppb
2017-11-13	3761-802-1221	ND
2017-11-13	3761-803-1228	ND
2017-11-13	3761-804-1320	5.30 ppb
2017-11-13	3761-805-1248	ND
2017-11-13	3761-806-1343	ND
2017-11-13	3761-807-1043	ND
2017-11-13	3761-808-1127	4.20 ppb
2018-02-12	3761-801-1306	24.4 ppb
2018-02-12	3761-802-1222	ND
2018-02-12	3761-803-1234	2.50 ppb
2018-02-12	3761-804-1315	27.0 ppb
2018-02-12	3761-805-1249	23.8 ppb
2018-02-12	3761-806-1336	13.2 ppb
2018-02-12	3761-807-1148	ND
2018-02-12	3761-808-1351	8.40 ppb
2018-05-07	3761-801-1226	53.3 ppb
2018-05-07	3761-802-1242	27.1 ppb
2018-05-07	3761-803-1256	36.4 ppb
2018-05-07	3761-804-1337	62.9 ppb
2018-05-07	3761-805-1311	42.7 ppb
2018-05-07	3761-806-1406	8.00 ppb
2018-05-07	3761-807-1212	10.8 ppb
2018-05-07	3761-808-1101	16.2 ppb
2018-08-16	3761-801-0944	47.8 ppb
2018-08-16	3761-802-1018	23.7 ppb
2018-08-16	3761-803-1010	24.6 ppb
2018-08-16	3761-804-0955	48.2 ppb
2018-08-16	3761-805-1003	13.8 ppb
2018-08-16	3761-806-0934	12.1 ppb
2018-08-16	3761-807-0926	19.7 ppb
2018-08-16	3761-808-0913	25.1 ppb
2018-11-05	3761-801-1305	ND
2018-11-05	3761-802-1409	1.000 ppb
2018-11-05	3761-803-1353	1.000 ppb
2018-11-05	3761-804-1320	ND
2018-11-05	3761-805-1329	2.40 ppb
2018-11-05	3761-806-1216	ND
2018-11-05	3761-807-1229	ND
2018-11-05	3761-808-1050	2.60 ppb
2019-02-04	3761-801-1403	4.10 ppb
2019-02-04	3761-802-1252	ND
2019-02-04	3761-803-1308	5.00 ppb
2019-02-04	3761-804-1151	2.90 ppb
2019-02-04	3761-805-1336	12.9 ppb
2019-02-04	3761-806-1152	3.10 ppb
2019-02-04	3761-807-1430	ND
2019-02-04	3761-808-1033	4.50 ppb
2019-05-08	3761-801-1100	37.0 ppb
2019-05-08	3761-802-1022	10.7 ppb
2019-05-08	3761-803-1031	17.3 ppb
2019-05-08	3761-804-1048	35.8 ppb
2019-05-08	3761-805-1040	20.6 ppb
2019-05-08	3761-806-1003	7.50 ppb
2019-05-08	3761-807-1012	10.5 ppb
2019-05-08	3761-808-0951	12.4 ppb
2019-08-05	3761-801-1354	51.1 ppb
2019-08-05	3761-802-1240	13.8 ppb
2019-08-05	3761-803-1256	21.2 ppb
2019-08-05	3761-804-1343	47.6 ppb
2019-08-05	3761-805-1304	32.1 ppb
2019-08-05	3761-806-1133	9.80 ppb
2019-08-05	3761-807-1421	18.7 ppb
2019-08-05	3761-808-1433	8.40 ppb
2019-11-04	3761-801-1307	126.1 ppb
2019-11-04	3761-802-1412	36.8 ppb
2019-11-04	3761-803-1400	74.4 ppb
2019-11-04	3761-804-1322	123.0 ppb
2019-11-04	3761-805-1340	97.1 ppb
2019-11-04	3761-806-1213	27.5 ppb
2019-11-04	3761-807-1227	25.4 ppb
2019-11-04	3761-808-1040	13.1 ppb