EPA legal limit
No federal limit
Maximum Contaminant Level
EWG health guideline
4.9 ppb
Science-based, stricter target
IARC classification
Group 2B — possibly carcinogenic to humans
Cancer research classification
Health effects
Bromoform is classified as a possible human carcinogen (Group 2B) by IARC. Of the four TTHM compounds, it has the least epidemiological evidence for human carcinogenicity, which is reflected in its relatively higher EWG health guideline. Animal studies show liver tumours at high doses. It is also associated with central nervous system depression at very high concentrations.
Where it comes from
Forms when chlorine disinfects water containing high bromide concentrations — most prevalent in coastal water supplies and geologically bromide-rich groundwater. Also found in water treated with ozone where bromide is present, though ozonation generally reduces TTHM formation.
How it's regulated
No individual EPA MCL — regulated under the TTHM group limit of 80 ppb. EWG health guideline: 4.9 ppb. Typically detected at lower levels than chloroform, making it a smaller fraction of total TTHM in most inland water systems.
How to filter bromoform
Not all filters address bromoform. Look for independently certified filters — NSF International certification means the removal claim has been independently verified.
Frequently asked questions
What is bromoform?
Bromoform is a trihalomethane compound that forms primarily in water supplies with very high bromide levels. It is typically the least prevalent of the four TTHM compounds in most US water systems, though it can be significant in coastal or geologically bromide-rich areas.
What are the health effects of bromoform?
Bromoform is classified as a possible human carcinogen (Group 2B) by IARC. Of the four TTHM compounds, it has the least epidemiological evidence for human carcinogenicity, which is reflected in its relatively higher EWG health guideline. Animal studies show liver tumours at high doses. It is also associated with central nervous system depression at very high concentrations.
Is bromoform regulated in drinking water?
No individual EPA MCL — regulated under the TTHM group limit of 80 ppb. EWG health guideline: 4.9 ppb. Typically detected at lower levels than chloroform, making it a smaller fraction of total TTHM in most inland water systems.
Where does bromoform come from?
Forms when chlorine disinfects water containing high bromide concentrations — most prevalent in coastal water supplies and geologically bromide-rich groundwater. Also found in water treated with ozone where bromide is present, though ozonation generally reduces TTHM formation.
How do I remove bromoform from tap water?
The most effective methods for removing bromoform 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 bromoform in your water?
Enter your ZIP code to see the measured level in your specific utility.