EPA legal limit
No federal limit
Maximum Contaminant Level
EWG health guideline
0.06 ppb
Science-based, stricter target
Health effects
The additional four HAA9 compounds include brominated species that are generally considered to have equal or greater health concern than the chlorinated HAAs in HAA5. HAA9 was introduced as a monitoring requirement under UCMR4 (2018–2021) to build the data foundation for potential future regulation. Total HAA9 levels are often 20–50% higher than HAA5 levels in high-bromide water systems.
Where it comes from
Forms during chlorination of water containing both organic matter and bromide. The ratio of HAA9 to HAA5 indicates the bromide content of the source water — a high ratio suggests significant bromide influence from coastal groundwater, industrial discharges, or natural geological sources.
How it's regulated
No federal EPA MCL — HAA5 is currently regulated at 60 ppb. HAA9 was monitored under UCMR4 to inform future rulemaking. The EWG health guideline of 0.06 ppb is stricter than the HAA5 guideline, reflecting the additional carcinogenic burden of the four brominated compounds not included in HAA5.
How to filter haloacetic acids
Not all filters address haloacetic acids. Look for independently certified filters—NSF International certification means the removal claim has been independently verified.
Frequently asked questions
What is haloacetic acids?
HAA9 is an expanded measure of haloacetic acid disinfection byproducts that adds four more brominated compounds — bromochloroacetic acid, bromodichloroacetic acid, chlorodibromoacetic acid, and tribromoacetic acid — to the five already measured in HAA5. The nine-acid grouping captures total HAA exposure more completely, particularly in water supplies with elevated bromide where HAA5 undercounts true HAA exposure.
What are the health effects of haloacetic acids?
The additional four HAA9 compounds include brominated species that are generally considered to have equal or greater health concern than the chlorinated HAAs in HAA5. HAA9 was introduced as a monitoring requirement under UCMR4 (2018–2021) to build the data foundation for potential future regulation. Total HAA9 levels are often 20–50% higher than HAA5 levels in high-bromide water systems.
Is haloacetic acids regulated in drinking water?
No federal EPA MCL — HAA5 is currently regulated at 60 ppb. HAA9 was monitored under UCMR4 to inform future rulemaking. The EWG health guideline of 0.06 ppb is stricter than the HAA5 guideline, reflecting the additional carcinogenic burden of the four brominated compounds not included in HAA5.
Where does haloacetic acids come from?
Forms during chlorination of water containing both organic matter and bromide. The ratio of HAA9 to HAA5 indicates the bromide content of the source water — a high ratio suggests significant bromide influence from coastal groundwater, industrial discharges, or natural geological sources.
How do I remove haloacetic acids from tap water?
The most effective methods for removing haloacetic acids are: Activated carbon block filter, NSF 53 certified filter, Reverse osmosis (RO). Look for NSF-certified systems—independent certification confirms removal claims have been verified.
Is haloacetic acids in your water?
Enter your ZIP code to see the measured level in your specific utility.