What method is commonly used for measuring chlorine residual in water?

The colorimetric DPD method is commonly used for measuring chlorine residual in water due to its sensitivity and reliability. The DPD (N,N-diethyl-p-phenylenediamine) reagent reacts with free chlorine to produce a pink color. The intensity of this color is proportional to the concentration of chlorine in the water sample. By comparing the color change to a standard color chart or using a colorimeter, operators can quantify the chlorine residual accurately.

This method is favored in water treatment processes because it allows for real-time monitoring and is relatively simple to perform, making it practical for routine testing in various water sources. Moreover, it can effectively differentiate between free chlorine and total chlorine, providing essential information for water quality management.

Other methods mentioned, while useful in different contexts, do not specifically measure chlorine residual in the same way as the DPD method does. For example, spectrophotometry can also be used for various measurements but is not as commonly employed specifically for chlorine residual. Turbidity tests measure the cloudiness of water, and conductivity meters assess ionic content but do not provide information about chlorine levels. Thus, the colorimetric DPD method stands out as the standard for this particular application.