After a new pipeline has passed the bacteriological tests, the highly chlorinated water should be flushed until the water exiting the pipe has a chlorine residual of __________.

• A. no greater residual than the feed water
• B. zero
• C. equal to the feed water
• D. twice the feed water

Answer: (A)

After disinfecting a new pipeline, you flush to remove excess chlorine while keeping enough residual to protect the line. The water leaving the pipe should have a chlorine residual that is not greater than the chlorine residual in the feed water. This ensures you aren’t introducing higher chlorination downstream than what the supply already has, while still maintaining some residual for ongoing protection. Zero residual would remove all disinfection protection, which isn’t desirable, and flushing until it equals twice the feed water would over-chlorinate the system. So the guideline is to exit with a chlorine residual no greater than the feed water’s residual.