Haloacetic Acids (HAA5)
A group of five chemicals that form as byproducts when chlorine or other disinfectants react with organic matter in water.
Source
Created during the water treatment disinfection process.
Health Risk
Long-term exposure may increase the risk of cancer. Some studies link them to reproductive and developmental effects.
Filter Tip
An activated carbon filter can reduce haloacetic acids in your drinking water.
Haloacetic Acids (HAA5) are a group of five disinfection byproducts that form when chlorine or chloramine used to treat drinking water reacts with naturally occurring organic matter. The five regulated compounds are monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and dibromoacetic acid. HAA5 are typically found alongside trihalomethanes (TTHM) — both are regulated as disinfection byproducts under the EPA's Stage 2 D/DBP Rule.
The EPA has set a Maximum Contaminant Level of 60 parts per billion (ppb) for HAA5, measured as a running annual average.
Why Are Haloacetic Acids a Concern?
HAA5 are found in virtually every chlorinated water system in the United States. Health concerns include:
- Increased cancer risk — dichloroacetic acid and trichloroacetic acid are classified as possible human carcinogens
- Liver toxicity and liver damage at high exposure levels
- Possible reproductive effects including low birth weight and neural tube defects
- Kidney damage with chronic exposure
What Causes High HAA5 Levels?
Like trihalomethanes, HAA5 levels are influenced by the amount of organic matter in source water, water temperature, chlorine dose, and how long water sits in the distribution system. Systems that draw from rivers or lakes with high organic content tend to have higher HAA5.
How to Reduce HAA5 at Home
- Activated Carbon Filters: Effective at reducing most haloacetic acids
- Reverse Osmosis: Highly effective for HAA5 removal
- Whole-House Carbon Filtration: Reduces exposure from all water uses
Unlike trihalomethanes, haloacetic acids are not volatile, so they are not significantly reduced by boiling or letting water sit.
Haloacetic Acids (HAA5) Levels in US Cities
Based on verified municipal water quality reports (Consumer Confidence Reports) from 17 cities.
Detected Within Limits (17)
Frequently Asked Questions
What is the difference between HAA5 and TTHM?
Both are disinfection byproducts formed when chlorine reacts with organic matter, but they are different chemical groups. TTHMs include chloroform and bromoform; HAA5 includes five haloacetic acids. Both have separate EPA limits (80 ppb for TTHM, 60 ppb for HAA5).
Are haloacetic acids in water dangerous?
At levels below the EPA limit of 60 ppb, the cancer risk is low but not zero. Long-term exposure above the limit may increase cancer risk. An activated carbon filter provides an additional margin of safety.
Do water filters remove haloacetic acids?
Yes. Activated carbon filters (including quality pitcher filters) can reduce HAA5. Reverse osmosis systems are even more effective. Look for NSF/ANSI 53 certification for VOC reduction.