An understanding of bromate formation mechanisms is critical for minimization and control of bromate during ozonation. Bromate formation observed in different natural source waters in the presence of hydroxyl radicals scavenger indicate that bromate forms predominantly through free radical species strongly suggesting that bromate formation can be reduced or eliminated with the addition of radical scavenger such as methanol during drinking water treatment. Carbonate radicals formed in the presence of alkalinity have shown to act as secondary oxidants of bromine species. The effect of adding hydrogen peroxide and ammonia on bromate formation during ozonation has been evaluated.