A watertight collection system prevents excessive inflow and infiltration.

• A. infiltration only
• B. inflow and infiltration
• C. inflow only
• D. infiltration and backflow

Answer: (B)

A watertight collection system aims to minimize both sources of unwanted water entering the sewer. Infiltration is groundwater seeping into pipes and joints, while inflow is surface water from rain, yard drains, or sump pumps connected to the sewer. If you limit both, the system won’t be overwhelmed during wet weather, helping prevent overflows and reducing treatment plant loads. That’s why the best answer is that both inflow and infiltration are addressed. The other options miss either one of these water entry paths or introduce backflow, which isn’t what a watertight sewer focuses on.