This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Environment and health, Subject name: Social & Preventive Medicine
The method of choice for purification of highly polluted water on a large scale is - 
Select and explain. 
A. Boiling and chlorination, B. Chlorination only, C. Superchlorination followed by dechlorination, D. Ultraviolet light treatment
C: Superchlorination followed by dechlorination
Answer: C: Superchlorination followed by dechlorination 
Explanation: 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