The recommended concentration of free chlorine is

The chlorine demand of water is the difference between the amount of chlorine added to the water and the amount of residual chlorine remaining at the end of a specific period of contact (usually 60 min)The point at which chlorine demand of water is met is called the &;breakpoint chlorine&;Chlorine added beyond breakpoint chlorine is free chlorine (HOCl and OCl). The minimum recommended concentration of free chlorine is 0.5 mg/L for one hour.The free chlorine provides a margin of safety against subsequent microbial contamination such as may occur during storage and distribution.Park 23e pg: 715