Cities with the highest disinfection byproduct risk

Trihalomethanes (THMs) and haloacetic acids (HAAs) are regulated disinfection byproducts (DBPs): they form when chlorine or chloramine reacts with natural organic matter in rivers, lakes, and reservoirs. Long-term exposure above EPA limits is associated with elevated cancer risk. This page lists cities where our structured profiles explicitly call out THMs, HAAs, or disinfection byproducts in the issues field — not a fresh nationwide utility lab sort.

Utilities must disinfect — but oxidizing organic-rich surface water produces THMs and HAAs. Hot weather, algae, soil runoff, and long distribution-system residence times all raise DBP formation. Boiling concentrates DBPs; it does not remove them.

What helps at home: NSF/ANSI 53-certified carbon filters (pitcher or under-sink) reduce THMs and volatile DBPs when maintained on schedule. Reverse osmosis (NSF/ANSI 58) strips DBPs along with a wide range of other contaminants. Whole-house carbon can reduce shower inhalation exposure but requires proper sizing and replacement intervals.

DBP risk varies by sampling location and season. Enter your ZIP for utility-specific contaminant language, violations, and filter ideas tied to what we parse for your system.