Which step involves flushing out the heavily chlorinated water until the concentration is acceptable for domestic use?

• A. Pre-flushing
• B. Chlorination
• C. Final Flushing
• D. Sampling/Analysis

Answer: (C)

Final flushing is the step used to purge heavily chlorinated water after disinfection so the chlorine residual drops to acceptable levels for domestic use. After chlorine is added to disinfect the water, the distribution system can carry water with high chlorine levels. Flushing—rapidly changing the water by drawing it through taps or purge points—removes this overly chlorinated water from the system, ensuring the water that reaches households has a safe, palatable residual.

This differs from pre-flushing, which happens before disinfection to clear the pipes; chlorination is the step that introduces chlorine; and sampling/analysis is the verification step that checks chlorine levels and other water quality parameters to determine when flushing can stop.