Tolyltriazole (TTA) has been widely used as a corrosion inhibitor for copper and copper alloy heat exchanger components in power plant cooling water systems. In this work the effectiveness of TTA protection in the presence of free chlorine, monochloramine, and ammonia was studied, in the context of using secondary treated municipal wastewater as cooling water. Results indicated that the corrosiveness of ammonia becomes negligible in the presence of TTA. Also, monochloramine represents a better disinfection agent in terms of copper corrosion protection by TTA than free chlorine. The packing density, film thickness, and number of layers of TTA adsorbed on the Cu surface were estimated from measurements and compared with estimates from other studies. It was found that copper can work as a catalyst for free chlorine to degrade TTA and that the surface packing density, film thickness, and number of layers increased in the presence of monochloramine.