What is the primary purpose of adding ammonia to drinking water?

The primary purpose of adding ammonia to drinking water is to create a combined chlorine residual. When ammonia is added to water that has already been chlorinated, it reacts with chlorine to form monochloramine. This compound is more stable than free chlorine, allowing for a longer-lasting disinfectant effect in the water distribution system. Monochloramine is used as a secondary disinfectant, helping to maintain a level of disinfection as water travels through pipes to consumers, thus reducing the risk of bacterial regrowth.

While the improvement of taste, reduction of bacteria, and increasing hardness may all be relevant in different contexts of water treatment, they are not the main reason for ammonia addition. The enhancement of flavor is typically not a consideration in water treatment processes. Similarly, ammonia does not directly reduce bacteria; rather, it serves to stabilize chlorine for effective disinfection. Lastly, increasing hardness is related more to the calcium and magnesium content of water rather than the inclusion of ammonia.