Inflow is the rapid flow of storm water into the sanitary sewer system. Storms or snow thaws bring large volumes of water into the system through:

  • Downspouts
  • Weeping tiles/foundation drains
  • Yard drains
  • Leaky manhole covers


Infiltration is the gradual downward flow of water from the surface of the earth into the soil and into the wastewater collection system.

High groundwater or water remaining in the soil after rain or snow could infiltrate wastewater lateral or mainline pipes, pipe joints and other parts of the wastewater collection system that might have deteriorated, cracked, sagged, or collapsed. This water seeps into the system from the surrounding soil.