A sewer backup is one of the most damaging things that can happen to a Toronto home. Sewage enters through floor drains, toilets, and sinks — contaminating finished basement space, destroying flooring and drywall, and creating a health hazard that requires professional remediation. The cleanup cost can exceed $20,000. A backwater valve, installed correctly, prevents the backup from entering the home in the first place. Toronto’s Basement Flooding Protection Subsidy can pay a large share of the installation cost.
This guide explains what a backwater valve is, how the installation works, and the exact steps to claim the city’s Basement Flooding Protection Subsidy.
What Is a Backwater Valve?
A backwater valve (also called a backflow preventer or sewer check valve) is a one-way valve installed in your home’s lateral sewer line — typically in the basement floor or under a concrete slab. It allows sewage to flow out of your home normally, but automatically closes when flow tries to reverse direction. When the city’s sewer system is overwhelmed during a heavy storm and sewage tries to back up through your lateral, the valve closes and the sewage has nowhere to go.
Without a backwater valve, the only thing standing between a surcharging sewer main and your basement is the water in your toilet traps.
Who Needs a Backwater Valve
Any Toronto home that has:
- A finished basement that would suffer significant damage in a flood
- A floor drain in the basement that could allow sewage entry
- A history of basement flooding or nearby flooding reports
- An older home in a neighbourhood with combined (storm and sanitary) sewers
- A home near the bottom of a slope or in a low-lying area
Toronto’s pre-war core and its post-war residential neighbourhoods were built over a combined sewer system — a single pipe carrying both storm water and sewage. During heavy rain events, that combined system can surcharge, pushing sewage backward through laterals throughout an entire neighbourhood at the same time. Backwater valves protect individual properties against the surge.
How the Installation Works
Installing a backwater valve is a plumbing job that requires opening the floor, typically in the basement, to access the lateral sewer line. The process:
- Camera inspection of the lateral. Before installation, we camera the existing sewer lateral to confirm its size, material, and condition. A cracked or root-infiltrated lateral affects the installation method and may need to be addressed first.
- Building permit. The City of Toronto requires a building permit for a backwater valve, and the subsidy depends on it. We pull the permit on your behalf.
- Floor opening. The basement concrete floor is cut open above the lateral, typically a 1–2 square foot opening. The cut section is removed and set aside for patching after installation.
- Valve installation. The backwater valve is inserted into the lateral and secured. Modern valves include a clear inspection window so you can verify the flap is seated correctly without opening the valve.
- City inspection. The valve has to pass a City inspection before it is covered, so the inspection comes before the floor is closed. We coordinate the inspection appointment.
- Floor patch. Once the valve passes, concrete is poured to patch the floor opening, leaving the valve’s access cover in reach so it can be checked and cleaned.
A typical installation takes 4–6 hours. Access to the basement and shutting off the water for a portion of that time is required.
Toronto’s Basement Flooding Protection Subsidy
The City of Toronto’s Basement Flooding Protection Subsidy Program pays back part of the cost of eligible flood-protection work. The City expanded the program on May 1, 2026. For work completed on or after November 12, 2025, a backwater valve qualifies for 80 per cent of the invoiced cost, up to $1,600 per valve, for up to two valves, including an alarm. Work completed before November 12, 2025 falls under the old limit of $1,250 for one valve.
The program covers several measures, up to $6,650 per property in total:
- Backwater valve: up to $1,600 each, two maximum
- Sump pump: up to $2,250, plus up to $300 for a battery backup
- Home plumbing assessment by a licensed plumber: up to $500
- Foundation drain (weeping tile) severance and capping: up to $400
Each property has a lifetime maximum for each type of work. Funding is first-come, first-served and depends on yearly City Council approval, so applying does not mean you will be paid.
Who Can Apply
- The registered owner of a single-family home, duplex, triplex or fourplex in Toronto.
- Your downspouts must be disconnected from the sewer (or you have a City exemption), and any front-yard parking pad must meet the zoning by-law.
- You must have no unpaid taxes or other debts owed to the City when the application is processed.
- Your contractor, and any sub-contractor, must hold a valid City of Toronto business licence (such as a plumbing or drain contractor licence) when the work is done. You can check a licence with the City’s Business Licence Lookup or by calling 416-392-6700.
How to Claim the Subsidy
- Have the valve installed under a building permit, and have it inspected by the City before it is covered. You must agree to give the City access and to allow photos or video of the valve.
- Get the original electronic invoice from each contractor. It must show the contractor’s name and address, your property address, the completion date, the cost of each device or service listed separately, and the total marked “paid in full”.
- Apply online through the City’s Basement Flooding Protection Subsidy application within two years of the installation.
- Allow up to 10 weeks for processing. Incomplete applications are not processed, so check every document before you submit.
Questions about your property’s subsidy history go to BasementFlooding@toronto.ca or 416-338-7668. Source: City of Toronto, Basement Flooding Protection Subsidy Program, checked October 2026.
We give you the itemised invoice and permit documentation the City requires when we complete the job. You submit the claim; the City issues the reimbursement to you directly.
How Much Does a Backwater Valve Cost in Toronto?
The installed cost of a backwater valve in a Toronto home typically ranges from $1,500 to $3,500, depending on:
- The depth of the lateral and how much concrete needs to be cut
- The condition and size of the existing lateral (a 4-inch PVC lateral is straightforward; an old 6-inch clay lateral in poor condition adds complexity)
- Whether a camera inspection is included separately or as part of the installation
With the City of Toronto subsidy covering up to $1,600, the net cost to a homeowner is typically $300–$1,900 for a standard installation. If a sump pump is also installed in the same job, both subsidies can be claimed together (up to $1,600 for the valve and up to $2,250 for the pump – learn more about sump pump installation in Toronto).
Backwater Valve vs. Sump Pump: What’s the Difference?
These two devices protect against different types of water entry and work best together:
- Backwater valve: stops sewage from backing in through the lateral sewer during a surcharge event. Does nothing for overland water (water entering through window wells, cracks in foundation walls, or at-grade entry points).
- Sump pump: pumps groundwater and overland water out of the basement through a dedicated discharge pipe. Does nothing to stop sewage backup through the sewer lateral.
During a major storm, both threats can occur simultaneously — the city sewer surcharges (sewage wants to come in through the drain) while overland flow and groundwater also rise (water wants to come in through the foundation). A property with only one of the two devices is only half-protected. Toronto’s subsidy is designed to encourage installation of both: the maximum per property is $6,650 because the intent is a combined solution.
Backwater Valve Maintenance
A backwater valve only protects you if its flap can close. Debris, grease or a rodent can hold it open, and a valve that has been ignored for years may fail on the one night it is needed.
- Look through the clear cover every few months, and always in spring and before the fall storm season. The flap should move freely, with nothing caught under it.
- Keep the access cover clear. Do not tile, carpet or box it in; you need to be able to reach it.
- Keep grease, wipes and food waste out of the drains. They build up in the valve body just as they do in the pipe.
- Test the alarm, if your valve has one, each time you check the cover.
- During a heavy storm, use as little water as you can. While the valve is closed, water from your sinks, shower, toilet or washing machine has nowhere to go and can back up into your own basement.
If the cover is cracked, the flap is stuck, or there is debris in the valve body you cannot reach, call a plumber rather than forcing it open. A damaged seal means the valve will not close properly.
Is a Backwater Valve Right for My Home?
Not every Toronto home is a candidate. Homes on a split sewer system (sanitary and storm separated) in newer developments have a different risk profile than homes on the older combined system in the city core. The lateral condition also matters: a severely deteriorated clay lateral may need lining or replacement before a backwater valve can be installed into it.
The first step is a camera inspection of your lateral. We assess the pipe’s condition, confirm whether a backwater valve installation is appropriate, and give you an honest quote for the full scope of work. If you’ve had a basement backup before, or if you’re in one of Toronto’s known flooding corridors, the camera inspection is worth doing regardless — it shows you the actual state of the lateral sewer under your property.
Backwater Valve Questions
Do I need a permit to install a backwater valve in Toronto?
Yes. The City of Toronto requires a building permit, and the valve must pass a City inspection before it is covered. The permit and the passed inspection are also conditions of the Basement Flooding Protection Subsidy.
How much will the City of Toronto pay for a backwater valve?
For work completed on or after November 12, 2025, the subsidy is 80 per cent of the invoiced cost, up to $1,600 per valve, for up to two valves. Work completed before that date is limited to $1,250 for one valve.
How long do I have to apply for the subsidy?
For work completed on or after November 12, 2025, you have two years from the installation to apply online. Work completed before that date had a one-year deadline.
Can I flush the toilet when the backwater valve is closed?
Try not to. A closed valve stops sewage coming in, but it also stops your own waste water going out. During a heavy storm, hold off on laundry, showers and flushing until the sewer level drops, or the water you use can back up into the basement.
Will a backwater valve stop all basement flooding?
No. It only stops sewage coming back through the sewer pipe. Water coming in through foundation cracks, window wells or rising groundwater needs a sump pump and good grading. Many Toronto homes need both, and the City subsidises both.
Book a Backwater Valve Assessment
ED Plumbing installs backwater valves throughout Toronto, Scarborough, North York, and Etobicoke. We pull the required permit, complete the installation to code, coordinate the city inspection, and provide the invoice documentation you need for the subsidy application.
Call (437) 260-6342 to book a lateral camera inspection and backwater valve assessment. We can usually schedule same-week for non-emergency assessments, and we give you a full flat-rate quote before any work begins.