What does 'water age' refer to in a distribution system, and how can it affect chlorine residual?

• A. The time water has spent in the distribution system since leaving the treatment facility; older water can have lower chlorine residuals.
• B. The age of the pipes.
• C. The shelf-life of the disinfectant.
• D. The time since the last water main repair.

Answer: (A)

Water age is the time water has spent in the distribution system after leaving the treatment facility. As water travels through pipes, the chlorine residual diminishes because it reacts with organic and inorganic matter and is consumed by biofilms and microorganisms. The longer the water has been in the system, the more opportunity there is for this decay, so older water tends to have a lower chlorine residual. Factors like temperature, flow, stagnation, and pipe materials can influence how quickly chlorine is lost. The other options don’t describe the time water has spent in the system or its effect on chlorine residual.