Which one of the following is the level of residual free chlorine recommended for swimming pool water disinfection?: (A) 0.5 mg/litre, (B) 0.8 mg/litre, (C) 1 mg/litre, (D) 5 mg/litre
Answer is C. Chlorination is the most widely used method of pool disinfection. Various workers have stated that continuous maintenance of 1mg/litre(1ppm) of free residual chlorine provides adequate protection against bacterial and viral agents. Park's Textbook of Preventive and Social Medicine, 25th edition, Page No. 788