What it means
Inflow is stormwater entering quickly through sources like roof drains, sump pumps, or open cleanouts. Infiltration is groundwater seeping through cracks, joints, laterals, or manholes. Both add flow that can overload sewers, lift stations, and treatment plants.
What operators watch
- Wet-weather flow patterns help identify I&I problems.
- Smoke testing, dye testing, flow monitoring, and CCTV can support investigations.
- Reducing I&I can prevent overflows and free treatment capacity.
Common exam traps
- Using inflow and infiltration interchangeably.
- Ignoring private laterals as a possible source.
- Focusing only on the plant instead of the collection system.
Field example
A lift station that runs constantly after rainfall may indicate inflow, infiltration, or both in its upstream basin.
