What is the role of residual chlorine in the distribution system?

• A. To maintain disinfection throughout the system and control microbial growth.
• B. To adjust pH.
• C. To color the water.
• D. To remove turbidity.

Answer: (A)

Residual chlorine in the distribution system acts as ongoing disinfection, keeping a protective barrier as water travels from the treatment plant to customers. After the initial disinfection at the plant, chlorine remaining in the water helps suppress microbial growth, inactivates microbes that may enter or grow in pipes, and prevents regrowth in storage and network components. Operators monitor this residual level to verify that the disinfectant is present throughout the system and to detect any loss of protection before water reaches customers. This protective residual is typically referred to as free chlorine or total chlorine, reflecting how much disinfectant is available downstream. It’s not used to adjust pH, color the water, or remove turbidity, which are addressed by other treatment steps.