Residual chlorine in chlorination of water should be:
The minimum recommended concentration of free chlorine is 0.5 mg/L for one hour. The sum of the chlorine demand of the specific water plus the free residual chlorine of 0.5 mg/L constitutes the correct dose of chlorine to be applied. The chlorine has no effect on spores, protozoal cysts and helminthic ova, except in higher doses. Ref: Park's Textbook of Social and Preventive Medicine, 19th edition, Page 575.
1 mg/L after 1 hr
0.5 mg/L after 1 hr
1 mg/L after 30 mins
0.5 mg/L after 30 mins