Bromate is a DBP (disinfection byproduct) that forms from ozonation of water and in certain cases chlorination, especially in bright sunlight.
According to Water Technology Magazine, Volume 32, Issue 1 - January 2009, Bromate is "an inorganic ion, bromate (Br03–)." It is a disinfection byproduct (DBP) that forms when the naturally occurring bromide ion (Br–, a form of the element bromine which, like chlorine, is a strong oxidant) reacts with ozone (O3):
It is tasteless and colorless. It is an issue mainly in regards to the ozonation of water. "In ozonation of water, the rate and extent of bromate formation depends upon the concentration of ozone used, the bromide ion concentration, pH and contact time. The reaction rate increases with increasing pH and levels off at about pH 8.8."
Ingestion of large amounts of bromate in drinking water is unlikely. In large amounts it can cause nausea, diarrhea, vomiting and abdominal pain. It affects the kidneys, the nervous system, and hearing.
The US Environmental Protection Agency (EPA) has set the maximum contaminant level (MCL) for bromate in public water systems at 10 parts per billion (ppb).
There have been scattered recalls of bottled water due to elevated bromate levels, and in 2007 Los Angeles had to drain 600 million gallons of water from its reservoirs due to excessive bromate formation.
As for treatment, there essentially is none. Bromate is best controlled by limiting its formation."Lowering pH to less than 8, adding ammonia or controlling ozone reaction time and the ozone/dissolved organic carbon ratio have been recommended, although these methods can have disadvantages as well."Sources: US EPA, New York State Department of Health, World Health Organization. Water Technology Magazine.