As the quantity of chlorine in the standard in order to kill the germs. Typically, the free residual chlorine at the 20-minute touch time must not be less than 0.3 – 0.5 mg/L.
The amount of chlorine in the disinfection. Typically, the free chlorine residual at the 20-minute exposure time must be not less than 0.3 - 0.5 mg / L.