What parameter is used to assess the effectiveness of chlorine in water treatment?

The parameter that is best used to assess the effectiveness of chlorine in water treatment is the residue level. Chlorine is a powerful disinfectant used to eliminate pathogens in drinking water, and its effectiveness hinges on maintaining an adequate concentration after it's added to the water supply.

Measuring the residual chlorine level allows operators to determine how much of the chlorine remains available to combat bacteria and other harmful microorganisms after its contact with water. A proper residual level ensures that there is enough chlorine present to continue providing disinfection as the water moves through the distribution system to consumers.

In contrast, while pH level, temperature, and flow rate are relevant factors that can affect chlorine's performance, they do not directly measure its effectiveness. For instance, pH can impact the disinfection efficiency of chlorine, but it does not indicate how much chlorine is still present. Similarly, temperature and flow rate affect reaction kinetics but are not indicative of residual chlorine levels in the water. Therefore, monitoring the residue level offers a clear and measurable reflection of the chlorine's disinfection capacity in the treatment process.