How often should the distribution residual for chlorine (both free and total) be monitored and recorded?

Monitoring and recording the chlorine residual in water distribution systems is vital for ensuring water safety and regulatory compliance. The correct frequency for monitoring, every hour, strikes a balance between maintaining sufficient oversight and managing resources effectively.

Chlorine residuals are essential indicators of the disinfectant's remaining efficacy in preventing microbial growth in the water supply. Measuring every hour allows for timely detection of any deviations in chlorine levels that could pose a public health risk, without overwhelming resources with excessive sampling.

Frequent monitoring helps in identifying trends and potential issues while ensuring compliance with regulatory standards, which may vary but typically require regular reporting of chlorine levels. While more frequent measurements, such as every 5 or 15 minutes, may provide additional data points, they might not be practical for all systems. Daily monitoring might fail to catch fluctuations that could occur between tests. Thus, an hourly frequency is often seen as the industry standard.