Bromate
BrO₃⁻·Affects kidneys, liver
Forms when ozone disinfection meets bromide in source water. Classified as a probable human carcinogen and tightly regulated at 10 parts per billion.
BrO₃⁻
EPA limit
0.010 mg/L (MCL)
Most at risk
Long-term consumers, residents on ozonated supplies with high source bromide
Found in
City water
AquaOx filters
YesActivated carbon
What it does to you
Health effects
Bromate is classified by the EPA as a probable human carcinogen (Group B2) and by IARC as a Group 2B possible carcinogen, based on consistent evidence of kidney and thyroid tumors in long-term animal studies. The kidneys and liver are the primary target organs.
Acute exposure at very high levels causes nausea, abdominal pain, and oxidative damage to red blood cells, but those exposures are not realistic from regulated drinking water. The MCL of 10 micrograms per liter (0.010 mg/L) is set conservatively to manage lifetime cancer risk.
Bromate is not volatile, so the main exposure route is direct ingestion through drinking and cooking water.
Where it comes from
How it gets into your water
Bromate forms when utilities disinfect water with ozone (O₃) and the source water contains naturally-occurring bromide. The ozone oxidizes bromide to bromate, and the resulting compound is stable, so once formed it stays in the water all the way to the tap.
Ozonation is favored by some utilities because it produces fewer THMs and HAAs than chlorination. The tradeoff is bromate when the source water is brackish or has trace bromide, which is more common in coastal regions and areas drawing from groundwater near saltwater intrusion.
Ozone disinfection
Ozone oxidizes naturally-occurring bromide
Distribution system
Stable byproduct, persists from plant to tap
Tap water
Direct ingestion in drinking and cooking water
Find out for yourself
Is it in your water?
Bromate only appears in systems that use ozone disinfection, which is less common than chlorine but increasingly used in larger metro systems. Your annual Consumer Confidence Report (CCR) will list it if your utility ozonates. Bottled water can also contain bromate, since most bottlers use ozone.
Levels vary by source-water bromide concentration. Utilities in coastal cities or those drawing from sources affected by saltwater intrusion typically run higher than inland systems.
The fix
How AquaOx filters it
Activated carbon, including the catalytic and coconut-shell stages used in AquaOx systems, reduces bromate through a combination of adsorption and chemical reduction (bromate is reduced back to bromide on the carbon surface).
Because AquaOx is whole-house, every tap in the home gets bromate-free water, which matters for households making baby formula, brewing coffee, or filling pet bowls where ingestion accumulates over time.