Chlorine is added to pool water to kill germs, viruses, and other harmful microorganisms, which helps to prevent the spread of diseases. Chlorine also helps to keep the water clear by preventing algae growth and helps to break down dirt, debris, or other substances in the water, keeping the pool safe for enjoyment. When chlorine is added to pool water, it forms a weak acid called hypochlorous acid that kills bacteria like salmonella and E. coli, as well as germs that cause viruses such as diarrhea and swimmer’s ear. Chlorine is a disinfectant that provides a “residual” level of protection against germs in the water. Chlorine is not the only sanitizer used in pools, but it is the most common and effective one. Chlorine is added to the water to kill germs, but it does not work right away. If used properly, free chlorine can kill most germs within a few minutes. Pool managers strive to keep the “free chlorine” level of pool water between about one and three parts per million. Maintaining the chlorine level in that range depends on several factors, including the pH of the water, which should be between 7.2 and 7.8.