Abstract: The description relates to an abrasion-resistant carrier catalyst for removing the nitrite and/or nitrate content of polluted water with selective nitrogen formation. The catalytically active metal component is palladium and/or rhodium or palladium and a metal from the copper group. The carrier consists of aluminum oxide in the "theta" and "kappa" modification and has either one maximum pore diameter in the 70 to 150 nm (700 to 1500 .ANG.) range or two maxima in the 10 to 150 nm (100 to 1500 .ANG.) range. The description also relates to a continuously operable process for the removal or reduction of the oxygen, nitrite and/or nitrate content of water by catalytic hydrogenation. The process is implemented using the novel carrier catalysts, the carriers being made of aluminum oxide of the theta and kappa modifications. Contamination of the catalyst is effectively prevented by the preferred use according to the fluidized bed process.