Total trihalomethanes (TTHMs)
Coachella Water Authority
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.
Samples
Samples exceeding legal limit (MCL)
Samples exceeding
health guidelines
Testing results - average by year
| Year | Average result | Samples taken | Detections | Range of results |
|---|---|---|---|---|
| 2014 | 0.511 ppb | 12 | 8 | ND - 0.890 ppb |
| 2015 | 0.538 ppb | 16 | 11 | ND - 1.40 ppb |
| 2016 | 0.535 ppb | 16 | 10 | ND - 1.40 ppb |
| 2017 | 0.471 ppb | 16 | 10 | ND - 1.10 ppb |
| 2018 | 0.600 ppb | 16 | 8 | ND - 4.60 ppb |
| 2019 | 0.999 ppb | 16 | 7 | ND - 6.00 ppb |
ppb = parts per billion
State and national drinking water standards and health guidelines
EWG Health Guideline 0.15 ppb
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.
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 |
|---|---|---|
| 2014-04-07 | 4790-804-0845 | 0.890 ppb |
| 2014-04-07 | 4790-803-0815 | 0.860 ppb |
| 2014-04-07 | 4790-802-0745 | ND |
| 2014-04-07 | 4790-801-0715 | 0.880 ppb |
| 2014-07-07 | 4790-804-0857 | 0.680 ppb |
| 2014-07-07 | 4790-803-0920 | 0.500 ppb |
| 2014-07-07 | 4790-802-0840 | ND |
| 2014-07-07 | 4790-801-0815 | 0.540 ppb |
| 2014-10-06 | 4790-804-0845 | ND |
| 2014-10-06 | 4790-803-0830 | 0.890 ppb |
| 2014-10-06 | 4790-802-0755 | ND |
| 2014-10-06 | 4790-801-0815 | 0.890 ppb |
| 2015-01-12 | 4790-802-0815 | ND |
| 2015-01-12 | 4790-803-0930 | 0.780 ppb |
| 2015-01-12 | 4790-804-0900 | ND |
| 2015-01-12 | 4790-801-0838 | 1.10 ppb |
| 2015-04-13 | 4790-804-0945 | 0.520 ppb |
| 2015-04-13 | 4790-803-0925 | 0.750 ppb |
| 2015-04-13 | 4790-802-0750 | ND |
| 2015-04-13 | 4790-801-0810 | 0.770 ppb |
| 2015-07-13 | 4790-801-0840 | 0.660 ppb |
| 2015-07-13 | 4790-802-0825 | ND |
| 2015-07-13 | 4790-803-0930 | 0.610 ppb |
| 2015-07-13 | 4790-804-0915 | 0.640 ppb |
| 2015-10-12 | 4790-804-0725 | 0.620 ppb |
| 2015-10-12 | 4790-803-0900 | 0.750 ppb |
| 2015-10-12 | 4790-801-0830 | 1.40 ppb |
| 2015-10-12 | 4790-802-0756 | ND |
| 2016-01-11 | 4790-803-1000 | 0.830 ppb |
| 2016-01-11 | 4790-802-0850 | ND |
| 2016-01-11 | 4790-804-0940 | ND |
| 2016-01-11 | 4790-801-0920 | 1.40 ppb |
| 2016-04-14 | 4790-802-0815 | ND |
| 2016-04-14 | 4790-803-0845 | 0.560 ppb |
| 2016-04-14 | 4790-801-0830 | 1.10 ppb |
| 2016-04-14 | 4790-804-0905 | 0.550 ppb |
| 2016-07-11 | 4790-802-0755 | ND |
| 2016-07-11 | 4790-801-0810 | 1.000 ppb |
| 2016-07-11 | 4790-803-0850 | ND |
| 2016-07-11 | 4790-804-0835 | 0.590 ppb |
| 2016-10-10 | 4790-803-0945 | 0.670 ppb |
| 2016-10-10 | 4790-802-0830 | ND |
| 2016-10-10 | 4790-801-0850 | 1.10 ppb |
| 2016-10-10 | 4790-804-0950 | 0.760 ppb |
| 2017-01-09 | 4790-803-1130 | 0.620 ppb |
| 2017-01-09 | 4790-804-1115 | 0.690 ppb |
| 2017-01-09 | 4790-802-1100 | ND |
| 2017-01-09 | 4790-801-1030 | 0.850 ppb |
| 2017-04-10 | 4790-804-0900 | ND |
| 2017-04-10 | 4790-803-0845 | ND |
| 2017-04-10 | 4790-802-0815 | ND |
| 2017-04-10 | 4790-801-0830 | 0.940 ppb |
| 2017-07-10 | 4790-803-0920 | 0.690 ppb |
| 2017-07-10 | 4790-802-0830 | ND |
| 2017-07-10 | 4790-804-0900 | 0.850 ppb |
| 2017-07-10 | 4790-801-0810 | 1.10 ppb |
| 2017-10-10 | 4790-801-0915 | 0.700 ppb |
| 2017-10-10 | 4790-802-0850 | ND |
| 2017-10-10 | 4790-804-0940 | 0.540 ppb |
| 2017-10-10 | 4790-803-0930 | 0.560 ppb |
| 2018-01-08 | 4790-801-0850 | 0.900 ppb |
| 2018-01-08 | 4790-804-0950 | 0.520 ppb |
| 2018-01-08 | 4790-802-0825 | ND |
| 2018-01-08 | 4790-803-0910 | 0.690 ppb |
| 2018-04-16 | 4790-804-0830 | 0.540 ppb |
| 2018-04-16 | 4790-802-0800 | ND |
| 2018-04-16 | 4790-803-0900 | ND |
| 2018-04-16 | 4790-801-0730 | ND |
| 2018-07-06 | 4790-801-1320 | ND |
| 2018-07-06 | 4790-804-1425 | ND |
| 2018-07-06 | 4790-802-1400 | ND |
| 2018-07-06 | 4790-803-1335 | 0.550 ppb |
| 2018-10-05 | 4790-801-1220 | 4.60 ppb |
| 2018-10-05 | 4790-803-1230 | 1.20 ppb |
| 2018-10-05 | 4790-804-1255 | 0.600 ppb |
| 2018-10-05 | 4790-802-1200 | ND |
| 2019-01-14 | 4790-803-1003 | ND |
| 2019-01-14 | 4790-804-0746 | ND |
| 2019-01-14 | 4790-801-0936 | 2.00 ppb |
| 2019-01-14 | 4790-802-0906 | ND |
| 2019-04-22 | 4790-804-1025 | 6.00 ppb |
| 2019-04-22 | 4790-803-1340 | 0.730 ppb |
| 2019-04-22 | 4790-801-1255 | 0.710 ppb |
| 2019-04-22 | 4790-802-1100 | 4.20 ppb |
| 2019-07-15 | 4790-804-1100 | ND |
| 2019-07-15 | 4790-803-1145 | ND |
| 2019-07-15 | 4790-802-1120 | ND |
| 2019-07-15 | 4790-801-0910 | 0.740 ppb |
| 2019-10-07 | 5810-804-0830 | ND |
| 2019-10-07 | 5810-803-0800 | ND |
| 2019-10-07 | 5810-801-0730 | 1.60 ppb |
| 2019-10-07 | 5810-802-0900 | ND |