What is I&I?

Inflow and infiltration (I&I) are terms used to describe the ways that groundwater and stormwater enter into dedicated wastewater or sanitary sewer systems. Dedicated wastewater lines are designed to transport wastewater from sanitary fixtures inside your house or place of business to the wastewater treatment plant. Sanitary fixtures include: 

  • Bathtubs
  • Lavatories
  • Showers
  • Sinks
  • Toilets


Inflow is stormwater that enters into the sanitary wastewater system. Various sources contribute to inflow, including: 

  • Downspouts
  • Drains from Driveways
  • Drains from Window Wells
  • Groundwater/Basement Sump Pumps
  • Improperly Installed or Maintained Footing/Foundation Drains
  • Outdoor Basement Stairwells
  • Roof Drains or Leaders

Stormwater should flow into the stormwater drainage system or allowed to soak into the ground and not cross into the wastewater pipe system.


Infiltration is groundwater that enters sanitary sewer systems through cracks and/or leaks in the sanitary sewer pipes. Cracks or leaks in sanitary sewer pipes or manholes may be caused by:

  • Age Related Deterioration
  • Damage or Root Infiltration
  • Installation or Maintenance Errors
  • Loose Joints
  • Poor Design

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1. What is the purpose of smoke testing?
2. What is I&I?
3. Is the smoke harmful?