Which of the following is a common inflow source into a sewer system?

• A. Roof leaders
• B. Defective manhole walls
• C. Cracked pipes
• D. Bad pipe joints

Answer: (A)

Inflow is water from outside the sewer entering through direct connections or surface runoff, especially during rain. Roof leaders (the downspouts from roofs) are a common inflow source because they channel rainwater directly into the sewer system when it drains from buildings, increasing flow during wet weather.

The other options involve water entering through the sewer from the surrounding ground or through cracks, not from surface runoff. Defective manhole walls, cracked pipes, and bad pipe joints allow groundwater or soil water to seep into the sewer—this is infiltration, not inflow. While they raise sewer flow, they originate from the surrounding environment rather than from direct rainfall-connected drainage.

So, roof leaders are the typical inflow source.