Disinfection Byproducts (TTHM & HAA5)
Also known as: Trihalomethanes, Haloacetic acids, DBPs, TTHM, HAA5
The trade-off of disinfection itself: chlorine kills pathogens but forms cancer-linked byproducts, making DBPs one of the most widespread health-based violations.
TTHM 0.080 mg/L · HAA5 0.060 mg/L. Total trihalomethanes (TTHM) and five haloacetic acids (HAA5) are the two regulated DBP groups.
Long-term exposure is associated with increased bladder cancer risk and possible reproductive and developmental effects. These are chronic risks measured as running annual averages, not acute hazards.
Formed inside the treatment and distribution system when chlorine or chloramine reacts with natural organic matter in the source water. Higher in warm water and systems with long pipe residence times.
At home, an activated-carbon filter reduces DBPs. Systems control them by removing organic matter before disinfection, optimizing chlorine dose, and managing water age in the pipes.
Source: EPA Safe Drinking Water Information System (SDWIS) · 2026 Q1
Disinfecting water saves lives by killing pathogens — but chlorine and chloramine also react with leaves, soil, and other organic matter to form trihalomethanes and haloacetic acids. Managing that trade-off is one of the central challenges of modern water treatment.
Because DBPs form throughout the distribution system, they're especially stubborn for systems with warm water, lots of organic matter, or long pipe networks. TTHM and HAA5 together are among the most common health-based violations nationwide.
States with the most disinfection byproducts violations
Community water systems with a related health-based violation since 2016.
Common questions
What is the EPA limit for disinfection byproducts in drinking water?
TTHM 0.080 mg/L · HAA5 0.060 mg/L. Total trihalomethanes (TTHM) and five haloacetic acids (HAA5) are the two regulated DBP groups.
Is disinfection byproducts in drinking water dangerous?
Long-term exposure is associated with increased bladder cancer risk and possible reproductive and developmental effects. These are chronic risks measured as running annual averages, not acute hazards.
Where does disinfection byproducts in water come from?
Formed inside the treatment and distribution system when chlorine or chloramine reacts with natural organic matter in the source water. Higher in warm water and systems with long pipe residence times.
How do I remove disinfection byproducts from my water?
At home, an activated-carbon filter reduces DBPs. Systems control them by removing organic matter before disinfection, optimizing chlorine dose, and managing water age in the pipes.
Which states have the most disinfection byproducts violations?
Across U.S. community water systems, 4,670 have had a related health-based violation since 2016, led by Texas with 638.
Source: EPA — National Primary Drinking Water Regulations
Source: EPA — Stage 2 Disinfectants and Disinfection Byproducts Rule