What is a common sign that chlorine disinfection is effective?

A common sign that chlorine disinfection is effective is the reduction in coliform bacteria. Chlorine is widely used in water treatment because of its ability to kill bacteria and other pathogens, making water safe for consumption. The presence of coliform bacteria, which are indicators of fecal contamination, suggests that harmful microorganisms may be present. Therefore, a significant reduction in these bacteria after chlorine treatment indicates that the disinfection process is working effectively.

The other options do not directly correlate with the effectiveness of chlorine disinfection. Turbidity refers to the cloudiness of water, which could be caused by suspended particles but does not imply successful disinfection. Increased hardness refers to the concentration of minerals like calcium and magnesium in water, and while it may impact water quality, it is unrelated to the presence of pathogens or the effectiveness of chlorine. A change in water temperature may also occur for various reasons but does not serve as a reliable measure of disinfection efficacy. Therefore, the reduction in coliform bacteria is the most relevant and definitive indicator of successful chlorine disinfection.