Infiltration & Inflow

Infiltration and Inflow (I/I) (PDF) is the collective name given to the unpermitted discharge that enters the Public Sanitary Sewer System such as:

  • Condensate
  • Groundwater
  • Roof runoff
  • Stormwater
  • Subsurface drainage
  • Surface water
  1. Definitions
  2. Impact
  3. How You Can Help


Infiltration is groundwater that enters the sewer system through sanitary sewer defects such as:

  • Cracks
  • Deteriorated manholes
  • Lateral defects
  • Leaky connections/joints
  • Root intrusion
  • Other locations where groundwater can seep into the system


Inflow is stormwater that enters the sewer system through a direct connection. Direct connections include:

  • Downspouts
  • Driveway drains
  • Foundation drains
  • Missing cleanout caps
  • Missing manhole lids
  • Sump pumps
  • Other permitted connections