What is the proper procedure for flushing a new cold water line before commissioning?

• A. Isolate line, open fixtures sequentially starting from the closest to the main, flush until clear and free of debris, then test for color/odor.
• B. Turn on all fixtures at once and flush for a few minutes.
• C. Use chemical cleaners to remove debris before testing.
• D. Flush only at the furthest fixture; ignore others.

Answer: (A)

Flushing a new cold water line before commissioning should be done in a controlled, staged way so debris and sediments are cleared from the pipe and the water quality is verified before the system is put into service. Isolating the line keeps the flushing focused on that specific run, preventing cross-flow from other circuits and giving a clear path for any particles to exit. Opening fixtures one by one starting with those closest to the main supply lets you purge the line section by section—from the connection point outward—until the water runs clear and free of debris. This approach also helps purge any trapped air as you progress. Once you’re confident the line is clear, testing for color and odor confirms the water quality meets expectations before commissioning.

Turning on all fixtures at once can create turbulence and push debris unpredictably, making it harder to ensure cleanliness. Using chemical cleaners is not appropriate for a potable-water system at commissioning, since you’d then need thorough rinsing and safety checks. Flushing only the farthest fixture ignores the rest of the line, leaving potential debris or contaminants in the upstream sections.