Total Trihalomethanes (TTHM)
Also reported as: chloroform, bromodichloromethane, dibromochloromethane, bromoform
What it is
A group of four chemicals (chloroform, bromodichloromethane, dibromochloromethane, bromoform) that form when chlorine reacts with natural organic matter in water. Levels are usually higher at the far ends of a distribution system and in warm months.
Your body
According to EPA, long-term exposure above the federal limit has been linked to liver, kidney, or central nervous system problems and an increased risk of cancer. Studies have associated long-term exposure to chlorination byproducts with bladder cancer.
Your home
Trihalomethanes do not affect plumbing. They can also be inhaled during hot showers.
Federal standard: MCL 80 ppb (locational running annual average, EPA)
Treatment options that can reduce it
Research & sources (4)
Maryland water systems that reported total trihalomethanes
- Baltimore City Department of Public WorksBaltimore City (also serves most of Baltimore County) · 2025 data
- City of AnnapolisAnne Arundel · 2025 data
- City of CambridgeDorchester · 2025 data
- City of FrederickFrederick · 2025 data
- City of SalisburyWicomico · 2025 data
- Easton UtilitiesTalbot · 2025 data
- Harford County Department of Public WorksHarford · 2025 data
- Howard County Department of Public WorksHoward · 2025 data
- Town of OxfordTalbot · 2025 data
- Town of St. MichaelsTalbot · 2025 data
- Town of TrappeTalbot · 2025 data
- WSSC WaterMontgomery and Prince George's · 2025 data
The information on this site is for general education only and is not medical advice. Talk with a qualified health professional about health concerns. Water treatment equipment performance depends on the system, its certification, and proper maintenance.
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