Recommended level of residual chlorine for disinfection of water is:-

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 mg/L Piped water supply: 0.5 mg/L Wells & sand-pots: 1 mg/L.