Where It Comes From
Byproducts of drinking-water disinfection; includes chloroform, bromodichloromethane, dibromochloromethane, and bromoform [1][2].
How You Are Exposed
Drinking tap water; breathing vapors during showers, baths, and indoor pools; absorption through skin during bathing/swimming [2][3].
Why It Matters
Over many years, higher TTHM levels are associated with increased bladder cancer risk; high exposures can affect the liver, kidneys, and nervous system. Some TTHMs are classified as possible carcinogens [1][2][4].
Who Is at Risk
People who drink a lot of tap water, pregnant people and fetuses, frequent long/hot shower or indoor pool users, and those with existing bladder-cancer risk factors [2][3].
How to Lower Your Exposure
Use certified activated carbon or reverse osmosis filters for drinking water; ventilate bathrooms and keep showers shorter; use cold water for drinking/cooking; review your water system’s Consumer Confidence Report and follow local notices [1][2][5].
References
- [1]U.S. EPA. National Primary Drinking Water Regulations: Disinfection Byproducts (Total Trihalomethanes).
- [2]WHO. Guidelines for Drinking-water Quality (4th ed., with 1st addendum): Trihalomethanes.
- [3]ATSDR. ToxFAQs: Chloroform.
- [4]IARC Monographs. Chloroform; Bromodichloromethane (Group 2B).
- [5]U.S. EPA. Drinking Water Treatability Database: Trihalomethanes (GAC/RO effectiveness).