EPA legal limit
No federal limit
Maximum Contaminant Level
EWG health guideline
0.2 ppb
Science-based, stricter target
IARC classification
Group 2A — probable human carcinogen
Cancer research classification
Health effects
DCA is classified as a probable human carcinogen (Group 2A) by IARC — the only individual HAA compound in this higher-risk tier. It has shown liver tumours, lung tumours, and reproductive effects in animal studies. In human epidemiological research, high HAA5 exposure has been associated with adverse pregnancy outcomes, and DCA is believed to be a key contributor. DCA has also been shown to be teratogenic (causing birth defects) in animal studies at doses above those typically found in drinking water.
Where it comes from
Formed during water chlorination when chlorine reacts with humic and fulvic acids naturally present in source water. Higher in warm weather and in utilities drawing from surface water with elevated organic matter. Levels vary seasonally.
How it's regulated
No individual EPA MCL — regulated as part of the HAA5 group standard of 60 ppb. EWG health guideline: 0.1 ppb, based on a 1-in-1-million cancer risk. NYC levels (2021–2023): part of the 38.2 ppb total HAA5 detected, which is 382× the EWG guideline.
How to filter dichloroacetic acid
Not all filters address dichloroacetic acid. Look for independently certified filters—NSF International certification means the removal claim has been independently verified.
HAA compounds including DCA are not removed by water ionization. NSF 53 certified activated carbon block filtration is required.
Frequently asked questions
What is dichloroacetic acid?
Dichloroacetic acid (DCA) is the most health-concerning of the five haloacetic acid compounds in the HAA5 group. It forms when chlorine reacts with natural organic matter in source water. DCA is also the most studied individual HAA for carcinogenicity and reproductive toxicity.
What are the health effects of dichloroacetic acid?
DCA is classified as a probable human carcinogen (Group 2A) by IARC — the only individual HAA compound in this higher-risk tier. It has shown liver tumours, lung tumours, and reproductive effects in animal studies. In human epidemiological research, high HAA5 exposure has been associated with adverse pregnancy outcomes, and DCA is believed to be a key contributor. DCA has also been shown to be teratogenic (causing birth defects) in animal studies at doses above those typically found in drinking water.
Is dichloroacetic acid regulated in drinking water?
No individual EPA MCL — regulated as part of the HAA5 group standard of 60 ppb. EWG health guideline: 0.1 ppb, based on a 1-in-1-million cancer risk. NYC levels (2021–2023): part of the 38.2 ppb total HAA5 detected, which is 382× the EWG guideline.
Where does dichloroacetic acid come from?
Formed during water chlorination when chlorine reacts with humic and fulvic acids naturally present in source water. Higher in warm weather and in utilities drawing from surface water with elevated organic matter. Levels vary seasonally.
How do I remove dichloroacetic acid from tap water?
The most effective methods for removing dichloroacetic acid 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 dichloroacetic acid in your water?
Enter your ZIP code to see the measured level in your specific utility.