At what pH level does chlorine destroy bacteria most rapidly?

The rate at which chlorine effectively destroys bacteria is greatly influenced by the pH level of the water. Chlorine is most efficient as a disinfectant at a pH around 7.5. At this pH, chlorine exists as hypochlorous acid (HOCl), which is the form of chlorine that has the highest germicidal activity. At pH levels below 7.5, the concentration of hypochlorous acid increases, enhancing its disinfection capability. However, as the pH rises above 7.5, the proportion of hypochlorite ion (OCl-) increases, which is less effective for disinfection purposes. Therefore, maintaining a pH around 7.5 maximizes chlorine’s effectiveness in rapidly destroying bacteria in water. This is critical for ensuring safe drinking water and effective water treatment processes.