Bromate formation can be attributed to three general pathways, two of whichrequire free bromine as an intermediate. Ammonia will react with free bromine tobromamines, which do not lead to bromate. Ammonia therefore, blocks two of thethree bromate formation pathways, but the third remains open, theoreticallyallowing some bromate to form regardless of the ammonia concentration. The amountof ammonia needed to block the free bromine pathways in experiments using purewater was observed to be very low: about 0.05 mg/L as nitrogen. However, ammoniais oxidized to nitrate during ozonation, and once ammonia is gone from thesystem, bromate can form via all three pathways. It is predicted that ammoniarequirements to inhibit bromate formation would therefore be controlled by theamount needed to ensure that a small residual is maintained throughout the ozonecontactor. The rate of ammonia oxidation in a given water can be determined usingsimple demand tests, allowing the amount of ammonia initially required forbromate minimization to be calculated. Includes 10 references, figures.