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 system 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 connected 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 services 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 recent years, portions of the sanitary wastewater collection and treatment systems have experienced higher-than-normal flows due to storm water entering the sanitary system. These flows exceed the system’s design capacity and create operational challenges, increase costs, and pose risks to private property and the environment.
To address these issues, the municipality as implemented several initiatives.
- In 2022, a multi-year CCTV inspection program of the sanitary sewer system was initiated to identify areas of inflow and infiltration (I&I) within the municipal infrastructure. This program focused on locating deficiencies in the municipal system, and did not include identifying illegal connections.
- Based on the results of these inspections, a remediation program began in 2023 to correct significant infrastructure deficiencies contributing to excess flows.
- Also in 2022, the City retained T.Y. Lin to complete a Water and Wastewater Servicing and Capacity Master Plan. This study evaluated existing servicing constraints and established long-term strategies for water and wastewater servicing. As part of this work, additional flow monitoring studies were conducted, which confirmed concerns related to inflow and infiltration. The recommendations from this master plan have informed the City’s long-range financial planning and capital planning strategy, ensuring that wastewater infrastructure upgrade can support both current needs and future growth.
- Operationally, the City’s Water & Wastewater Division continues to inspect wastewater collection infrastructure, including maintenance holes (manholes), to identify and address infiltration issues. The City also installs rain bladders in maintenance hole lids in low-lying roadway areas to prevent storm water inflow during wet weather events.
- In 2025, the City introduced additional incentive to reduce illegal storm water connections. Building permit application fees were waived for permits specifically related to plumbing modifications required to disconnect storm water sources (such as sump pumps or foundation drains) from the municipal sanitary sewer system.
Frequently Asked Questions about wastewater and storm water discharge
What is inflow and infiltration?
Inflow and infiltration (I&I) occurs when stormwater or groundwater enters the sanitary sewer system. Sanitary sewers are designed to carry wastewater from homes and businesses to treatment plants. Stormwater from rain and melting snow should enter storm sewers or soak into the ground.
When extra water enters sanitary sewers, it can overload the system and cause problems such as sewer backups, higher treatment costs and environmental risks.
What is a surcharged sanitary sewer?
A sanitary sewer becomes surcharged when the amount of water flowing through it exceeds its capacity. This often happens during heavy rain or rapid snowmelt when extra stormwater enters the sanitary system.
When pressure builds up in the pipe, wastewater may try to escape through the lowest points in the system, including floor drains or plumbing fixtures in basements.
How can surcharged sanitary sewers cause basement flooding?
Basement flooding can occur when the water level in a surcharged sewer rises above the level of plumbing fixtures in a home. Wastewater can then flow backward through pipes and enter the basement through floor drains, toilets or other fixtures.
What are some examples of illegal connections?
Illegal connections allow stormwater to enter the sanitary sewer system. Examples include:
- Roof downspouts connected to sanitary pipes
- Sump pumps connected to sanitary sewers
- Foundation or footing drains connected to sanitary pipes
- Damaged or defective house sewer lines that allow groundwater to enter
Do illegal connections really add that much water?
Yes. Even a small number of illegal connections can have a large impact. For example, a typical sanitary sewer pipe can handle wastewater from more than 200 homes. However, only a few sump pumps running at full capacity can overload the same pipe during heavy rain.
Why is it important to remove illegal connections?
Removing illegal connections reduces the amount of stormwater entering the sanitary sewer system. This helps:
- reduce the risk of sewer backups and basement flooding
- lower the cost of wastewater treatment
- protect the environment by reducing the risk of wastewater overflows
What can I do if my sump pump or downspout is connected to the sanitary sewer?
Stormwater from sump pumps and downspouts should be directed away from the house and allowed to drain into the yard, a ditch or another safe drainage area on your property. If changes to plumbing are required to disconnect stormwater sources from the sanitary sewer system, Kawartha Lakes currently waives building permit fees for this work.
How can I help prevent basement flooding?
One of the best ways to protect your home is by installing a backwater valve on your sanitary sewer line. A backwater valve prevents wastewater from flowing back into your home during sewer surcharges.Kawartha Lakes offers a Backwater Valve Subsidy Program to help residential property owners reduce the risk of basement flooding. Residents should also make sure sump pumps, roof downspouts and foundation drains are not connected to the sanitary sewer system.
I’ve never had basement flooding. Why should I remove my illegal connections?
Even if your home has never flooded, stormwater from your property may still be entering the sanitary sewer system and contributing to sewer surcharges elsewhere in the community. Removing illegal connections helps protect your neighbours, reduces strain on wastewater infrastructure, and lowers the risk of environmental impacts.