What is the most common method for testing chlorine residuals in small systems?

The DPD test is the most common method for testing chlorine residuals in smaller water systems due to its reliability, efficiency, and simplicity in use. The DPD (N,N-diethyl-p-phenylenediamine) test involves adding a reagent to a water sample that reacts with free and combined chlorine to produce a pink color proportional to the chlorine concentration. This color change allows for easy visual assessment or can be measured using a spectrophotometer for more precise quantification.

This method is widely adopted because it does not require extensive laboratory equipment or procedures, making it suitable for smaller systems, which often operate with limited resources. The DPD test is also versatile, as it can be used for both low and high chlorine residuals, providing an effective means for operators to monitor disinfection levels consistently.

In contrast, alternative methods like ion chromatography and the SPADNS test may involve more complex procedures or specialized equipment, making them less practical for routine testing in smaller systems. The colorimetric method is somewhat broader and can refer to several techniques, but the DPD method specifically is a well-established standard in the industry for measuring chlorine residuals.