How often should total residual chlorine levels be checked in the distribution system?

Total residual chlorine levels should be checked every 5 minutes in the distribution system to ensure that chlorine levels remain within acceptable limits that prevent bacterial growth and maintain water quality. This frequent monitoring is crucial because chlorine is a key disinfectant used to ensure that drinking water is safe. Rapid changes in chlorine levels can occur due to various factors, such as water demand changes, variations in water temperature, or the presence of organic material, all of which can impact the effectiveness of disinfection. By checking chlorine levels every 5 minutes, water quality analysts can quickly identify and respond to any issues, ensuring that water is safe for consumption and compliant with health regulations.

The other options reflect longer intervals that may delay necessary interventions if chlorine levels drop or rise unexpectedly, potentially compromising public health and safety.