Bromochloromethane in Drinking Water
Found in 801 water systems • disinfection_byproducts
Updated September 2026 • Data from EWG & EPA
What is Bromochloromethane and Why Does It Matter?
# Bromochloromethane in Your Tap Water: What You Need to Know
Bromochloromethane is a chemical byproduct created when water treatment plants disinfect tap water with chlorine and bromine. When these disinfectants react with naturally occurring organic matter in water—like decaying leaves and soil compounds—they form trihalomethanes (THMs), a group of chemicals that includes bromochloromethane. This isn't a chemical added intentionally to poison your water. It's an unintended consequence of keeping water safe from bacteria and viruses. The irony is that the very process meant to protect you creates this contaminant. Bromochloromethane enters your home through treated municipal water supplies, especially in areas with high chlorination practices and elevated organic matter in source water.
The health effects of bromochloromethane exposure depend on the level and duration of contact. At low exposures, research shows limited immediate harm. However, the Environmental Working Group (EWG) and other health organizations have raised concerns about chronic exposure. Studies suggest that long-term consumption of bromochloromethane may increase cancer risk, particularly for bladder and colorectal cancers, though the exact mechanisms are still being studied. The EPA classifies it as a possible human carcinogen. Children and pregnant women may face higher risks because their bodies are still developing and they consume more water relative to their body weight. The good news: most people exposed to bromochloromethane in tap water are exposed to very small amounts, and the absolute risk remains low for most communities.
Currently, the EPA sets a legal limit of 80 ppb (parts per billion) for total trihalomethanes, the group that includes bromochloromethane. This means individual bromochloromethane levels can be higher than that without violating federal law. The EWG, which uses more conservative health-based guidelines, recommends a maximum of 0.6 ppb for bromochloromethane—a much stricter standard. Our data shows that bromochloromethane was detected in 801 water systems across the country, with 243 systems exceeding the EWG guideline. The average level detected was 0.218 ppb, but some systems tested as high as 13.8 ppb—more than 23 times the EWG recommendation. This gap between EPA and EWG standards reflects ongoing scientific debate about what level is truly safe for families.
Texas, California, New York, New Jersey, and Oklahoma are the hardest hit, with Texas alone reporting bromochloromethane in 299 water systems. Texas's high occurrence likely stems from its warm climate, which increases organic matter in water sources, and its reliance on chlorination for disinfection. California's 124 affected systems reflect similar challenges in agricultural areas with high chlorine use. The Northeast—New York and New Jersey combined account for 78 systems—faces bromochloromethane issues partly because older water infrastructure and colder climates with seasonal organic matter fluctuations create ideal conditions for THM formation. Southwestern states like Oklahoma also show significant detection, likely due to drought-stressed water sources with concentrated organic compounds.
Removing bromochloromethane requires filtration methods that target organic compounds and chemical byproducts. Activated carbon filters are highly effective, removing up to 90% of bromochloromethane when properly installed and maintained. Reverse osmosis systems perform even better, removing 99% or more of this contaminant along with other THMs. Whole-home systems protect you during showering and cooking, while under-sink or pitcher filters work for drinking and cooking water specifically. If your water system reports bromochloromethane above 0.6 ppb, installing a carbon or reverse osmosis filter is a practical step. You can check your water quality report online—most municipalities publish annual reports showing detected contaminants. Testing your own water confirms whether filtration is needed for your specific situation. The goal isn't panic; it's informed protection for your family.
Regulatory Standards for Bromochloromethane
| Standard | Level | Notes |
|---|---|---|
| EWG Health Guideline | 0.06 ppb | Stricter, based on latest science |
| Average Detected Level | 0.22 ppb | Across all tested systems |
| Highest Detected Level | 13.80 ppb | Worst-case system |
Cities With the Highest Bromochloromethane Levels
| # | City | Detected Level | People Served |
|---|---|---|---|
| 1 | Unknown, MD | 13.80 ppb | 7,900 |
| 2 | Dallas, MT | 7.90 ppb | 650 |
| 3 | Fishkill, NY | 7.60 ppb | 2,000 |
| 4 | Lebec, CA | 6.88 ppb | 1,379 |
| 5 | North East, MD | 6.38 ppb | 8,600 |
| 6 | Newark, MD | 6.38 ppb | 2,154 |
| 7 | Pulaski, VA | 4.70 ppb | 100 |
| 8 | Mountain Lake Park, MD | 4.06 ppb | 0 |
| 9 | Ilwaco, WA | 3.67 ppb | 2,757 |
| 10 | 540-674-4803, VA | 3.10 ppb | 0 |
| 11 | Pulaski, VA | 3.10 ppb | 292 |
| 12 | Pulaski, VA | 3.10 ppb | 9,452 |
| 13 | Elizabeth, WV | 2.60 ppb | 2,289 |
| 14 | Perry Point, MD | 2.37 ppb | 0 |
| 15 | Kelley, IA | 2.20 ppb | 304 |
States Most Affected by Bromochloromethane
How to Remove Bromochloromethane From Your Water
Standard pitcher filters and refrigerator filters use activated carbon with insufficient contact time and capacity to effectively remove bromochloromethane. Reverse osmosis is required for reliable removal because THMs require either extended contact with high-quality GAC or membrane separation.
Standard pitcher filters and carbon-only filters do not reliably remove Bromochloromethane. A reverse osmosis system with NSF/ANSI 58 certification is the most reliable solution.
Effective removal requires reverse osmosis, point-of-use distillation, or whole-home granular activated carbon systems with proper sizing and maintenance. Standard activated carbon pitcher filters are insufficient.
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Shop Hydrogen FlaskFrequently Asked Questions
Is Bromochloromethane in my drinking water?
Bromochloromethane was detected in 801 water systems across the US. Check your city's water quality report to see if it affects your water supply.
What are the health effects of Bromochloromethane in water?
Bromochloromethane has been associated with various health concerns at elevated levels. The EWG has set health guidelines that are typically stricter than EPA legal limits.
Which city has the most Bromochloromethane in its water?
Based on our analysis, Unknown, MD has the highest detected levels of Bromochloromethane in its water supply.
How do I remove Bromochloromethane from my water?
Reverse osmosis (RO) systems are generally the most effective at removing this contaminant. Check the filtration recommendations section for specific guidance.
Related Contaminant Guides
Data sources: Environmental Working Group (EWG) Tap Water Database, U.S. EPA Safe Drinking Water Information System (SDWIS)
Last updated: September 2026
Methodology: Contaminant levels are compared against both EPA legal limits (Maximum Contaminant Levels) and EWG health guidelines, which are often stricter and based on the latest scientific research.
