To make safe drinking water, Dosatron ACS or NSF-certified metering pumps, installed in line with the water supply, inject a dose of chlorine (NaClo, CaClo) that allows the destruction of organic materials such as viruses and microbes in the water, in proportion to the flow rate. Since much of the chlorine is needed to neutralise these organic materials, the dose of chlorine dispensed by the metering pump will leave a portion, called free residual chlorine, available to treat possible future contamination of the water in the network or homes. This free chlorine ensures that the disinfection capacity remains. According to the WHO, the concentration of free chlorine in drinking water should be 0.2 to 0.5 mg/l.