Contaminant guide
Total trihalomethanes (TTHMs)
TTHMs form when chlorine disinfectant reacts with organic matter in the water. They are more common in surface-water systems.
Health context
Long-term exposure above the standard is associated with increased cancer risk and possible liver/kidney/central nervous system effects.
EPA standard notes
EPA MCL for TTHMs is 0.080 mg/L (80 µg/L) as a locational running annual average.
Standards and rules change—confirm on epa.gov/sdwa.
What you can do
- Check your CCR for disinfectant byproduct averages.
- Activated carbon filters can reduce some byproducts when certified and maintained.
- Never stop using disinfectant as directed during a boil-water notice.
FAQ
Is a filter required?
Not automatically. Many systems meet standards without point-of-use filters. Filters can be useful for taste, specific contaminants, or home plumbing issues—match certifications to the problem.
Where should I verify numbers?
Your utility’s Consumer Confidence Report, public notices, TCEQ resources, and EPA ECHO/SDWIS records.