Chlorination of water is which level of prevention -

Chlorine kills pathogenic bacteria but has no effect on spores and ceain viruses (e.g., polio, hepatitis) except in high doses It oxidises iron, manganese, it controls algae and slime organisms and aids coagulation. Disinfecting action of chlorine is mainly due to hypochlorous acid. Primary prevention is the action taken prior to the onset of the disease which removes the possibility of occurrence of disease. It includes sanitation, infection control, immunization, protection of food, milk, water supplies. The proper treatment of water by chlorination helps in infection control hence its a mode of primary prevention. Parks textbook of preventive and social medicine.K Park. Edition 25.page no:774