What is the minimum combined chlorine residual required throughout a water distribution system in mg/l?

The minimum combined chlorine residual required throughout a water distribution system is essential for maintaining effective disinfection and ensuring that the water is safe for consumption. A residual of 1.0 mg/l is often established as a standard because it is adequate to maintain disinfection while minimizing the formation of potentially harmful disinfection byproducts. This level helps to ensure that any pathogens that might enter the distribution system are adequately neutralized, contributing to the overall safety and quality of the drinking water supply.

Setting a minimum combined chlorine residual at this level also supports effective monitoring and operational control within the distribution system, allowing water treatment facilities to respond proactively to variations in water quality and potential contamination events. Lower levels might not provide sufficient protection against pathogens, and higher levels could lead to undesirable tastes, odors, and potential health concerns from byproduct formation. Thus, the choice of 1.0 mg/l reflects a balance between efficacy in disinfection and the maintenance of water quality.