Inflow and Infiltration

Inflow is water other than sanitary wastewater that enters a sewer system from sources such as roof leaders, cellar / foundation drains, yard drains, area drains, drains from springs and swampy areas, maintenance hole covers, cross connections between storm sewers and sanitary sewers, and catch basins.

Infiltration is water other than sanitary wastewater that enters a sewer system from the ground through defective pipes, pipe joints, connections or maintenance holes.

Inflow and Infiltration Problems

There are a number of problems caused by inflow and infiltration, including:

  • Basement flooding: Too much water in the sanitary system can cause water to back up into basements
  • Overflows into the environment: To prevent basement flooding during extreme wet weather events, a combination of storm water and wastewater is released into the environment to alleviate capacity. Learn about combined sewer overflows.
  • Reduced system capacity: Restricts available capacity for current residents and prospective future growth
  • Increased costs to residents: Excess flows of clean environmental water is needlessly collected, transported and treated at the wastewater treatment plants
  • Dilution in sanitary sewers: Reduces efficiency of treatment plants

Video: Inflow and Infiltration Introduction

Video: Impact of Rainwater on our Sanitary Sewer System

How You Can Help

We all have an important role to play in reducing the impacts of inflow and infiltration on our sanitary system. Look out for these common sources at home:

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