Chlorine is used as a disinfectant in water distribution systems. Three properties can be measured, free chlorine, combined chlorine and total chlorine. Free chlorine is a measure of the amount of the chlorine in the water that can be used for disinfection. Combined chlorine refers to the chlorine that has been “used up” and is no longer available for disinfection. Total chlorine is the sum of free and combined chlorine.
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