Chlorine is added to water as a disinfectant. The first reaction occurs when organic substances and metals present in water react with chlorine and transform into compounds that are unavailable for disinfection. The amount of chlorine used in these reactions is called the chlorine consumption of the water. The presence of free chlorine in drinking water indicates that sufficient chlorine has been added to the water to inactivate most bacteria and viruses. The water is protected from recontamination during transport to the house or during water storage in the household. Since the presence of free residual chlorine in drinking water indicates the probable absence of disease-causing organisms, it is used as one of the parameters of drinking water quality.
