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Unwanted Water in the Sewer System


​​​​Extra groundwater and rainwater in the sewer system – known as “inflow and infiltration”— can lead to sewer overflows into homes, businesses and the environment. Both local government and private property owners have a role to play in reducing inflow and infiltration.​​​



Sewer Overflows, Inflows, and InfiltrationSewer Overflows, Inflows, and Infiltration434894816

​​What is inflow and infiltration?

Inflow and infiltration (I&I) happens when extra groundwater and rainwater flows into sanitary sewers. Sanitary sewers are designed to carry wastewater from sinks and toilets. There is often some extra rainwater and groundwater in sanitary sewers, but aren’t made to handle large amounts of it.

This extra water enters sewers through:

  • Holes or cracks in pipes caused by damage, age or tree roots
  • Leaky pipe joints and maintenance covers
  • Roof and foundation drains that are improperly connected to a property’s sanitary sewer line

Some of this extra water gets in through municipal and regional sewers, but a lot of it also comes from pipes on private properties.



Inflow and Infiltration Fact Sheet, Inflow and Infiltration Fact SheetInflow and Infiltration Fact Sheet

Extra water ca​n overload sewers

A little extra water from individual properties may not seem like a big deal, but it can quickly add up to become more than the wastewater system was designed to handle. This can lead to sewer overflows into homes, businesses and the environment. This extra water is a particular challenge in the wet fall and winter months, especially as we start to see more atmospheric rivers due to climate change.

Learn more about sewer overflows​

What property owners can do

Property owners play a key role in reducing I&I: about half of our region’s sewer system is made up of pipes on private properties. Property owners have a responsibility to maintain the sewer lines on their property and make sure that nothing is improperly connected to those lines.

To stop large amounts of extra water from getting into your pipes:

  • Have your pipes inspected with a camera by a plumber or drainage specialist at least once a decade
  • Fix or replace old or damaged pipes, especially if they are “combined” sewer lines that carry both sanitary wastewater and stormwater
  • Ensure downspouts and foundation drains are not connected to your sanitary sewer pipe
  • Avoid planting water-loving trees or shrubs on top of your sewer line or drain pipes, as their roots can pry open joints between pipes

What Metro Vancouver is doing

Metro Vancouver is working with its member municipalities to reduce I&I by:

  • Helping identify neighbourhoods with high levels of I&I and working towards solutions for those areas
  • Upgrading infrastructure and planning for future growth, and conducting regular maintenance, to reduce the risk of future sewer overflows
  • Exploring ways to encourage fixing problems on private properties
  • Incorporating reduction targets and strategies into regional wastewater planning, including wet weather pricing to better allocate costs to those contributing to the problem ​

 Related links



Wastewater Testing and Environmental MonitoringWastewater Testing and Environmental Monitoring
What are Sewer Overflows?, What are Sewer Overflows?What are Sewer Overflows?
Stormwater and Drainage Management, Stormwater and Drainage ManagementStormwater and Drainage Management

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