Know Your Environment. Protect Your Health.

Total trihalomethanes (TTHMs)

Harris County Municipal Utility District 5

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.

 

48

Samples

0

Samples exceeding legal limit (MCL)

14

Samples exceeding
health guidelines

Testing results - average by year

 
YearAverage resultSamples takenDetectionsRange of results
2018ND80ND
20191.59 ppb82ND - 7.40 ppb
20202.39 ppb84ND - 8.20 ppb
20213.63 ppb82ND - 16.6 ppb
20221.73 ppb82ND - 7.20 ppb
20230.950 ppb84ND - 2.70 ppb

ppb = parts per billion

State, National, and Health Guidelines for Drinking Water

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
2018-02-06AE12481ND
2018-02-06AE12476ND
2018-05-02AE24794ND
2018-05-02AE24772ND
2018-09-12AE39788ND
2018-09-12AE39789ND
2018-11-26AE46811ND
2018-11-26AE46812ND
2019-02-06AE53171ND
2019-02-06AE53173ND
2019-04-29AE63920ND
2019-04-29AE63933ND
2019-08-15AE78899ND
2019-08-15AE78868ND
2019-12-04AE912185.30 ppb
2019-12-04AE912197.40 ppb
2020-02-21AE994882.20 ppb
2020-02-21AE995031.10 ppb
2020-05-20AF12101ND
2020-05-20AF12104ND
2020-08-19AF245468.20 ppb
2020-08-19AF245647.60 ppb
2020-10-22AF31655ND
2020-10-22AF31656ND
2021-02-02AF4213612.4 ppb
2021-02-02AF4213816.6 ppb
2021-06-18AF58799ND
2021-06-18AF58804ND
2021-08-12AF66047ND
2021-08-12AF66049ND
2021-10-28AF75038ND
2021-10-28AF75039ND
2022-02-15AF848667.20 ppb
2022-02-15AF848686.60 ppb
2022-04-25AF94216ND
2022-04-25AF94217ND
2022-09-16AG13475ND
2022-09-16AG13478ND
2022-11-30AG20270ND
2022-11-30AG20271ND
2023-02-13AG285811.40 ppb
2023-02-13AG285832.70 ppb
2023-05-09AG39709ND
2023-05-09AG39710ND
2023-07-24AG49767ND
2023-07-24AG49768ND
2023-11-15AG637241.000 ppb
2023-11-15AG637252.50 ppb