What should be the combined chlorine residual minimum level in a water treatment system?

The correct answer indicates that the minimum combined chlorine residual level in a water treatment system should be 0.6 mg/l. This level is important for ensuring effective disinfection and maintaining a certain quality of water throughout the distribution system. Combined chlorine, which forms when chlorine reacts with organic materials and ammonia in the water, serves to kill bacteria and other pathogens.

A minimum residual level of 0.6 mg/l is typically recommended to ensure that enough disinfectant is present to provide adequate microbial control. This level helps to prevent potential growth of harmful microorganisms within the distribution system and ensures that the water remains safe for consumption as it travels through pipes to consumers.

Striving for this specific minimum level also takes into account various factors, including the water's temperature, pH, and the presence of organic materials, all of which can affect chlorine's effectiveness as a disinfectant. Having a residual that falls below this level can significantly decrease the water system's ability to prevent microbial growth and compromise public health.