Know Your Environment. Protect Your Health.

Total trihalomethanes (TTHMs)

Harris County Municipal Utility District 321

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.

 

24

Samples

0

Samples exceeding legal limit (MCL)

8

Samples exceeding
health guidelines

Testing results - average by year

 
YearAverage resultSamples takenDetectionsRange of results
201811.7 ppb444.30 ppb - 18.9 ppb
201912.1 ppb448.80 ppb - 16.3 ppb
2020ND40ND
2021ND40ND
2022ND40ND
2023ND40ND

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
2018-01-11AE0891118.9 ppb
2018-04-04AE211724.30 ppb
2018-07-12AE3309714.3 ppb
2018-10-09AE429269.20 ppb
2019-01-31AE5241312.7 ppb
2019-04-18AE629618.80 ppb
2019-09-25AE8459710.6 ppb
2019-11-07AE8889316.3 ppb
2020-02-13AE98421ND
2020-05-28AF13051ND
2020-09-10AF26996ND
2020-12-15AF37656ND
2021-02-09AF43231ND
2021-05-18AF54346ND
2021-08-19AF67105ND
2021-11-16AF76782ND
2022-02-10AF84248ND
2022-04-21AF94017ND
2022-09-29AG15424ND
2022-10-25AG18300ND
2023-03-14AG32936ND
2023-05-18AG41055ND
2023-07-20AG49572ND
2023-12-05AG65465ND