What is a flush-and-fill procedure?

• A. Filling storage tanks with untreated water
• B. Isolating a storage tank to reduce pressure
• C. A cleaning method for storage tanks
• D. Flushing water through lines while reintroducing treated water to restore residuals after maintenance or sampling

Answer: (D)

Restoring disinfectant residuals in the distribution system after maintenance or sampling is the central idea. A flush-and-fill procedure means flushing water through the lines to remove stagnation and debris while reintroducing treated water so the disinfectant residual returns to acceptable levels. This helps keep the water safe as it moves through the system and prevents microbial growth. Filling with untreated water would defeat the purpose, and isolating a storage tank or treating it solely as a cleaning method describes different actions not focused on reestablishing residuals. The emphasis here is on flushing and refilling with treated water to reestablish the necessary residuals after maintenance or sampling.