What is chlorination and why is it used in water treatment?

Chlorination is the process of adding chlorine or chlorine compounds to water for disinfection. It kills or inactivates pathogenic microorganisms including bacteria, viruses, and some protozoa. Chlorine also provides residual disinfection in distribution systems. Common forms include chlorine gas, sodium hypochlorite, and calcium hypochlorite. Breakpoint chlorination ensures complete disinfection by oxidizing all ammonia.