Minimum recommended concentration of free chlorine drinking water at the end of 1 hour is -: (A) 0.5 mg/L, (B) 0.1 mg/L, (C) 1.0 mg/L, (D) 1.5 mg/L
Answer is A. The minimum recommended level of residual chlorine is 0.5 mg/L. Park's Textbook of Preventive and Social Medicine, 25th edition, Page No. 774