What is the preferred test for measuring residual chlorine in water?

The preferred test for measuring residual chlorine in water is the DPD test (N,N-diethyl-p-phenylenediamine test). This method is widely accepted because it provides a reliable and accurate measurement of free and total chlorine levels in water samples.

The DPD test works through a chemical reaction where chlorine reacts with DPD to produce a pink color in the solution, the intensity of which correlates with the concentration of chlorine present. The color can be measured photometrically, allowing for precise quantification of chlorine levels.

In contrast, the other tests listed are not as commonly used for residual chlorine measurement. The colorimetric test refers to techniques that might measure a variety of substances but does not specify chlorination, making it less targeted. The syringalazine test is primarily used for other applications, such as measuring certain types of environmental contaminants, and is not suitable for residual chlorine. The FACTS test may have applications in specific scenarios but is not recognized as a standard for residual chlorine measurement in water. Thus, the DPD methodology stands out as the most effective and widely utilized approach for assessing chlorine levels.