To balance disinfectant residuals with minimizing disinfection byproducts during seasonal demand swings, which approach is recommended?

• A. Increase dosing uniformly across all locations without adjustments.
• B. Maintain current dosing and ignore age and DBP formation.
• C. Adjust dosing strategy and locations, flush strategically, monitor water age, and consider process or treatment changes if allowed.
• D. Switch to a different disinfectant without evaluating DBPs.

Answer: (C)

Seasonal demand swings change how quickly water moves through the system and how long it sits in tanks and pipes, which in turn affects both disinfectant residuals and disinfection byproduct (DBP) formation. The best approach is to tailor disinfection rather than applying a single everywhere dose. By adjusting where and how much disinfectant is added, you can maintain protective residuals in critical parts of the system while reducing conditions that lead to high DBP formation. Strategic flushing helps replace older water, lowers stagnation, and brings residuals back to desired levels. Keeping an eye on water age ensures you’re not letting aged water travel long distances and accumulate more DBPs. If allowed, considering process or treatment changes to reduce DBP precursors or to optimize disinfection can further balance residual control with DBP minimization. The other options fall short because they ignore the impact of water age and distribution dynamics, or they substitute one concern for another without evaluating DBPs.