The method of choice for purification of highly polluted water on a large scale is -
Superchlorination followed by dechlorination comprises the addition of large doses of chlorine to the water and removal of excess of chlorine after disinfection. This method is applicable to heavily polluted waters whose quality fluctuates greatly. Park's Textbook of Preventive and Social Medicine, 25th edition, Page No. 775
Boiling and chlorination
Chlorination only
Superchlorination followed by dechlorination
Ultraviolet light treatment
Environment and health