What method is commonly employed to test for chlorine residual in water?

The method commonly used to test for chlorine residual in water involves the DPD (N,N-diethyl-p-phenylenediamine) test. This method is widely recognized for its reliability and ease of use in water treatment facilities. When DPD is added to a sample of water that contains free chlorine, it reacts to form a pink-colored compound, the intensity of which is proportional to the concentration of chlorine in the water. This colorimetric change allows for quantitative measurement of chlorine residual, providing an essential parameter for monitoring and controlling disinfection processes in water treatment.

This method is favored because of its sensitivity to low concentrations of chlorine and its ability to distinguish between free and total chlorine, contributing significantly to water quality management and ensuring safe drinking water. In contrast, HTH refers to a form of calcium hypochlorite used for disinfection, THM (trihalomethanes) is a group of byproducts formed during chlorination, and VOC (volatile organic compounds) refers to organic chemicals that can evaporate into the air, none of which are methods for measuring chlorine residual directly.