Which of the following is not a step in the recommended disinfecting sequence for a new water main?

• A. Pre-flushing
• B. Sampling/Analysis
• C. Final Flushing
• D. Backwashing with sediment filter

Answer: (D)

Disinfecting a new water main follows a sequence designed to remove debris and verify safety before service. Start with pre-flushing to push out loose sediments and reduce chlorine demand, then perform sampling/analysis to check disinfectant residuals and meet water-quality criteria, then complete final flushing to clear disinfectant and any remaining sediments so the water entering the system is safe. Backwashing with a sediment filter, on the other hand, is a filtration maintenance step used on treatment filters to clean the media by reversing flow, and it is not part of the main-line disinfection sequence. It doesn’t contribute to disinfecting the interior of the new main, so it isn’t included in the recommended sequence.