Inflow & Infiltration

The Town’s sewer system is comprised of two parts: storm sewers and sanitary sewers. Storm sewers properly manage excess water from rainfall, snowmelt or run off before discharging it to lakes and streams. Sanitary sewers carry wastewater from toilets, sinks and drains to treatment plants for processing before returning it to the environment.

Inflow and infiltration is the term used when water that should be entering the storm sewer system makes its way into a sanitary sewer. This can be caused by damaged sewer pipes and/or incorrectly connected sump pumps, downspouts, and building drains.

On this page: 
1. Why is inflow and infiltration a problem?
2. How severe is the issue?
3. What you can do to prevent inflow and infiltration
4. What is the Town doing about inflow and infiltration?
5. Frequently Asked Questions

Why is inflow and infiltration a problem?

Inflow and infiltration is a problem for a number of reasons:

  • It may cause sewage backups in basements
  • It puts excess stress on wastewater treatment plants and infrastructure
  • Wastewater treatment plants are designed to treat raw sewage, not sewage that has been diluted
  • It increases the costs to residents as the wastewater treatment plants are treating water that should be directed into the stormwater system

How severe is the issue?

The Craigleith and Thornbury Wastewater Treatment Plants each treat roughly 3,000,000 litres of sewage each and every year. On the wettest days of the year, where inflow and infiltration is most prevalent, the plants take in more than 10,500,000 litres of additional wastewater per day. That's enough additional wastewater to fill four Olympic swimming pools.

What you can do to prevent inflow and infiltration

There are a few things you can do to ensure your property doesn’t contribute to inflow and infiltration.

  1. Ensure your building drain or sump pump is no connected to the sanitary sewer system
  2. Ensure your downspouts flow onto your yard, or into a french drain or rain barrel
  3. Clear debris such as leaves and garbage blocking storm sewer grates
  4. Participate in inflow and infiltration reduction projects happening in your neighbourhood

Doing these things can help safeguard your property and protect the environment by reducing the likelihood of wastewater spills.

What is the Town doing about inflow and infiltration?

Finding and reducing inflow and infiltration is a high priority for the Town. It reduces sewage treatment costs, reduces wear on costly infrastructure and maximizes the capacity for wastewater to move through the system. 

Inspection, Identification and Enforcement

In areas where higher-than-normal wastewater flows have been identified, the Town will use different techniques to pinpoint the sources. Residents will be notified prior to any testing in their area.

Sewer Cameras - A CCTV camera is inserted into the sewer pipe to identify cracks and failed pipes.

Smoke Testing - A harmless, odourless smoke is pumped into the wastewater sewer system. The smoke travels through the system and exits out any improperly connected eavestroughs.

Dye Testing - A harmless dye is added to the storm sewer to determine if there is a direct connection to the wastewater sewer.

As sources of inflow and infiltration are identified, Town staff will work to find the best way to correct them. The Town will address any issues in the sewers that are owned by the Town, while homeowners will be responsible to correct any issues on their own property.

Should a homeowner choose not to correct a problem within a reasonable amount of time, the Town may choose to levy a fine.

Frequently Asked Questions