Old pipes should be cleaned if they show signs of ____________

• A. rusting
• B. mineral scale
• C. bacterial slime growth, deposits of iron bacteria, and tuberculation
• D. pitting corrosion

Answer: (C)

Old pipes should be cleaned when there is evidence of biofilm and tuberculation, meaning bacterial slime growth with deposits of iron bacteria and tuberculation on the pipe interior. This combination indicates a complex buildup of biological material plus mineral deposits that can harbor bacteria, increase surface roughness, reduce flow, and hinder disinfection effectiveness. Cleaning serves to remove both the slime and the mineral deposits, restore smoother flow, and improve water quality. Signs like rusting or pitting suggest corrosion, which requires different actions beyond cleaning, and mineral scale alone is just mineral buildup without the biological component that makes cleaning necessary in this context.