Preventing Inflow and Infiltration

What is inflow and infiltration?

Sanitary sewers collect wastewater from our homes, businesses and industries to take it to a wastewater treatment plant. Wastewater is collected using pipes buried in the Municipality's road allowance. Sanitary sewers are designed to only carry wastewater from sanitary systems to our wastewater treatment facilities. In comparison, storm water collection systems collect runoff from snow and rain and carry it from buildings, roadways, and the ground to a natural watercourse or body of water. This runoff is usually untreated. Wastewater and storm water systems are designed to transport only a certain volume of water. When more water than they are designed to handle is diverted into them, it can cause trouble. 

When property owners direct eavestroughs to municipal sanitary systems or connect private storm systems such as sump pump outlet pipes to them, it is known as an illegal connection. Doing this can cause a high volume of storm water to flow into wastewater collection and treatment systems instead of letting it flow into storm-water systems or soak into the ground. When too much water enters sanitary sewers, it can lead to problems for property owners, such as sewer back-ups. This is known as inflow and infiltration.

Installing a backwater valve within your house/building’s sanitary drainage plumbing can help protect your property. Backwater valves are usually installed in the basement of a building and are now mandatory on all new homes in serviced areas of the municipality. Additionally, disconnecting downspouts and sump pumps connected to the sanitary system and directing them onto the lawn away from the house can help. Today's subdivision construction standards consider storm water management and are designed to divert the water from sump pumps, roof drains, area drains. etc. to storm sewers, retention ponds or drainage ditches. Property owners should also check that their sanitary sewer cleanout cap is tightly installed. Loose or missing cleanout caps beneath the basement floor can let groundwater into sanitary collection systems. They are also a source of dangerous sewer gas. Once the cleanout cap is properly tightened, basement flooding may occur because groundwater can no longer escape into the sanitary sewer. However, the sump pump is designed to handle this groundwater and direct it away from the house. Make sure to check that your sump pump is working properly.

What is the municipality doing to prevent inflow and infiltration?

In 2017, an inspection of the Bayfield sanitary wastewater collection and treatment system found that the system was handling a larger volume of storm water than what is usually found in similar systems. These high flows are above the design capacity of the Bayfield sanitary system and lead to expensive operational challenges.

Since the discovery, the Municipality has started a program to educate property owners and tenants about the dangers of overloading sanitary collection systems. We have also been working to enforce the removal of “illegal” connections to the sanitary sewer system. If the Municipality suspects that a property has an unauthorized connection, property and building owners will be notified, and the removal of the unauthorized connection to the sanitary system will be required.

Starting in the spring of 2024, the by-law division will be conducting inspections on private properties to check for any improper and illegal connections, and to identify any properties/owners allowing storm water into the sanitary sewer system. These inspections are currently voluntary. However, any improper connections will be required to be removed.

If you’d like help determining if you’re unknowingly discharging storm water into the sanitary sewers, or for more information regarding backwater valves, please contact Aaron Stewardson, Manager of Development Services and Chief Building Official or Dave Kester, Manager of Public Works.

About the Municipal Inflow and Infiltration Inspection program

Review the following for more information on the Municipal Inflow and Infiltration Inspection (Miii) program. 

A municipal inflow and infiltration inspection is a check of discharge locations from downspouts, sump pumps (interior and exterior), exterior catch basins, cleanout locations and lids, and other plumbing elements for a building. Photographs will be taken to document the sources.

Currently, the Miii program is voluntary. We recognize that some owners may not realize that clean water is infiltrating the treatment system from their property. The Municipality is seeking full co-operation.

We are approaching this problem with education and proactive property inspections. We see laying fines as a last resort. Current fines are set at $500.00 under By-law 9-2020.

The program has already started. Watch for educational material wherever you get your information: social media, mailouts and news articles.

Properties of concern will be identified. A written notice containing details about an inspection, timeline, areas of concern and voluntary booking will be mailed to these properties.

The process will take months. We want to allow time for residents to learn about the problem and provide access to municipal staff when it suits you.

Discharging waste into the public sewage and storm works is prohibited by By-law 9-2020. The by-law authorizes the Municipality to inspect the discharge of waste into drains and sewers. The by-law can be found on our by-laws page. 

Frequently asked questions about wastewater and stormwater discharge

In this section, you will find more information about inflow and infiltration, as well as answers to frequently asked questions.

Sanitary sewers have been designed to transfer sanitary waste only. Too much storm water flow added to the normal sanitary flow can exceed the capacity of a sanitary sewer. This creates a situation where the sanitary sewer is “surcharged”. Basically, surcharging happens when the amount of flow trying to get through a pipe is higher than the maximum capacity of the pipe. This causes pressure to build up in the pipe. When pressure builds up, it tries to relieve itself through any means possible, one of which is by backing up private sanitary services and filling basements and crawlspaces.

Basement flooding can happen when a home has sanitary fixtures or floor drains that are at a lower elevation that the surcharge level because surcharged sanitary sewers flow at a higher than normal level.

Examples include:

  • Roof downspouts
  • Sump pumps
  • Defective house sanitary sewer lines
  • Footing/foundation drains tied to the house sanitary sewer lines

Removing illegal connections significantly reduces the flow of extra storm-related water into sanitary sewer systems. This reduces the amount of storm-water entering treatment facilities. It can significantly reduce the costs of operating the facility and limit sewer backups into basements.

Yes. For example, a typical 200 mm (eight-inch) diameter sanitary sewer can handle domestic sewage from up to 225 homes. However, it takes only five sump pumps operating at full capacity to overload the same sanitary sewer.

Sump pipes could be run overland to a ditch or swale which drains to another location. Also, a long flexible tube that can be moved around the yard to avoid soaking only one portion of the yard could be used. Sump pumps can be run underground through a 4” or 6” diameter perforated PVC pipe with holes at the bottom and backfilled with washed gravel. An overflow tube should be placed at the opposite end to allow the water to escape in the event that too much water flows through the pipe. This pipe can be located in a convenient area of the yard, such as a garden. Another option could be to run it to a drywell.

Note: Pipes flowing overland should be kept no farther than 10 feet from the house and should stop at the property line to avoid icy sidewalks in winter.

You may not have basement flooding due to surcharged sewers, but if your plumbing pumps or drains storm related water into the sanitary sewer, it could be the cause of flooding in your neighbour’s basement. By removing illegal connections and reducing storm-related flows to sanitary sewers, treatment costs—and ultimately wastewater rates—can be reduced.


Updates about inflow and infiltration and the municipal inspection program are presented to Council through reports. 

Helpful resources

Sump Pump Brochure (for an accessible alternative, contact the Development Services department)

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