<prompt> Recommended level of residual chlorine for disinfection of water is:-0.1 mgL for a contact period of half hour0.5 mgL for a contact period of half hour0.5 mgL for a contact period of 1 hour1.0 mgL for a contact period of 1 hour  <response>: Level of free residual chlorine recommended:- Water type RecommendedResidual chlorine level Contact period Drinking water to kill hepatitis A virus 1.0 mg per litre ppm 1 hour Drinking water to kill polio virus 2.0 mg per litre ppm 1 hour Drinking water to kill Cyclops 2.0 mg per litre ppm 1 hour 1 mg per litre 1 ppm Drinking water 0.5 mg per litre ppm 1 hour Water bodies, post disaster 0.7 mg per litre ppm 1 hour Swimming pool sanitation 1.0 mg per litre ppm 1 hour Also remember, After an epidemic of cholera, residual chlorine levels to be maintained are: At filling of tanker trucks :2 mgL Piped water supply: 0.5 mgL Wells sand-pots: 1 mgL. 