Total Trihalomethanes (TTHM)
disinfection byproduct
Byproduct formed when chlorine disinfectant reacts with natural organic matter in the water. Higher in surface-water systems.
EPA regulatory status
Legal limit (MCL)
80 ppb
Goal (MCLG)
Not set
MCL 80 ppb (0.080 mg/L), enforced as a Locational Running Annual Average (LRAA) under the Stage 2 D/DBP Rule — not an instantaneous limit. No MCLG for the group (individual trihalomethanes have their own MCLGs).
Health effects
Long-term exposure is associated with liver, kidney, or central-nervous-system problems and an increased risk of cancer (notably bladder cancer).
This is general public-health information, not medical advice — consult your physician with any health concerns.
National violations
98,123
EPA's enforcement data (SDWIS/ECHO) records 98,123 violations of Total Trihalomethanes (TTHM)'s rule nationally.
How to remove Total Trihalomethanes (TTHM)
Frequently asked questions
What is Total Trihalomethanes (TTHM)?
Total Trihalomethanes (TTHM) is a disinfection byproduct regulated in US drinking water. Byproduct formed when chlorine disinfectant reacts with natural organic matter in the water. Higher in surface-water systems.
What is the legal limit for Total Trihalomethanes (TTHM) in drinking water?
MCL 80 ppb (0.080 mg/L), enforced as a Locational Running Annual Average (LRAA) under the Stage 2 D/DBP Rule — not an instantaneous limit. No MCLG for the group (individual trihalomethanes have their own MCLGs).
What health effects does Total Trihalomethanes (TTHM) have?
Long-term exposure is associated with liver, kidney, or central-nervous-system problems and an increased risk of cancer (notably bladder cancer).
How many violations of Total Trihalomethanes (TTHM) limits are on record nationally?
EPA's enforcement data (SDWIS/ECHO) records 98,123 violations of Total Trihalomethanes (TTHM)'s rule nationally.
How do I remove Total Trihalomethanes (TTHM) from my water?
Filter technologies certified to reduce Total Trihalomethanes (TTHM) include: activated carbon (NSF/ANSI 53), reverse osmosis (NSF/ANSI 58). Look for a filter independently certified against the specific NSF/ANSI standard for this contaminant — general "reduces contaminants" marketing claims are not the same as a contaminant-specific certification.
Source: EPA National Primary Drinking Water Regulations · Data as of 2026-07-16