Last updated: October 17, 2026. Guidance checked against Government of Canada, Intact Centre on Climate Adaptation and City of Toronto pages on that date.
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Key takeaways
– Most spring basement leaks come from surface water: snowmelt and rain that sit against the foundation because of poor grading, short downspouts or clogged window wells.
– Start with the free and cheap fixes. The Intact Centre groups flood-protection work into three steps: maintenance ($0), simple DIY upgrades (under $250) and complex upgrades done with a contractor (over $250).
– Aim to move water at least 2 m (6 ft. 6 in.) away from your foundation, and grade the soil so it slopes away from the house.
– Water that comes up through the floor, a crack that keeps widening, or sewage backing up through a floor drain needs a professional, not caulk.
– In Toronto, the City’s expanded subsidy program can cover part of a backwater valve, sump pump, battery backup and a plumbing assessment, up to $6,650 per property.
Every spring across Ontario, a winter’s worth of snow melts in a few warm days while the ground underneath is still frozen, and rain arrives on top. If the ground slopes the wrong way or downspouts dump water beside the wall, that water ends up against your foundation, and some of it finds its way inside.
The most common causes are also the cheapest to fix. This guide helps you find the source, then works through fixes in order of cost and effort.
Why basements leak more in spring
The Government of Canada’s flood-prevention guidance explains it simply: when temperatures rise, meltwater from snowbanks around your foundation can enter your home, and the risk goes up when melt is combined with rain, and for older or poorly graded properties (Canada.ca: Clear snow and ice).
A few things make spring especially hard on a basement:
- Frozen ground drains slowly. Water that would normally soak into the soil runs across the surface instead and collects in low spots, often right beside the house where snow was piled all winter.
- Snowbanks against the wall. Shovelled or plowed snow stacked against the foundation melts directly onto it.
- Ice-clogged eavestroughs and window wells. Ice and snow in a window well can block its drain, so meltwater pools against the window (Canada.ca: Basement window maintenance).
- High groundwater. If the water table around your home rises, any crack in the foundation can let groundwater in (Canada.ca: Foundation maintenance).
- Overloaded sewers. During heavy rain, municipal sewers can become overloaded, and water can back up into basements through floor drains (City of Toronto).
Step 1: Figure out where the water is coming from
The fix depends on the source, so start here.
| What you see | Likely source | Where to start |
|---|---|---|
| Water at the base of a wall, worst after melt or rain | Surface water against the foundation | Grading, downspouts, snow clearing |
| Water running down from a basement window | Window well filling up, or failed caulking | Clear the well, check the seal, add a cover |
| A wet line along one crack in the wall | Water getting through the crack | Fix the outside water first, then seal the crack |
| Water seeping up through the floor or the floor-wall joint | Groundwater pressure under the slab | Talk to a pro about drainage and a sump pump |
| Dirty water coming up the floor drain | Sewer backup | Plumber; ask about a backwater valve |
| Damp walls with no visible water, worse in summer | Condensation, not a leak | Dehumidify and ventilate |
To tell condensation from a leak, tape plastic wrap tightly to the damp wall for a day or two: moisture on the room side suggests condensation; moisture behind it suggests water coming through.
Then go outside during a melt or rainstorm and watch where the water goes: toward the house, out of a downspout at the corner, or into a window well full of slush?
Step 2: Free fixes (maintenance you can do today)
The Intact Centre on Climate Adaptation calls these “maintain what you’ve got”: do-it-yourself, $0, and at least twice a year (Intact Centre: Three steps to cost-effective home flood protection).
- Move the snow. The Government of Canada recommends shovelling snow about 1 to 1.5 m (3 to 5 ft.) away from your foundation where possible, clearing snow and ice from window wells, and keeping snow off downspouts (Canada.ca: Clear snow and ice).
- Clear the eavestroughs. Clogged troughs overflow and dump roof water right at the foundation. Canada.ca recommends cleaning eavestroughs twice a year (Canada.ca: Actions to reduce flood damage).
- Clear the window wells. Remove leaves, dirt and ice by hand or with a wet-dry vacuum so water can drain into the gravel instead of pooling against the window.
- Clear the nearest storm drain or ditch so water can leave your street.
- Test your sump pump. Pour water into the pit and confirm the pump turns on and pushes water outside. The federal guidance recommends a full test once a year and checks during and after melt and heavy rain (Canada.ca: Sump pumps).
- Clear the floor drain and clean the backwater valve if you have one.
Step 3: Cheap DIY upgrades (under $250)
These are the Intact Centre’s “simple upgrades”: do-it-yourself work it puts at under $250 (Intact Centre).
Extend your downspouts
This is often the single best fix for a spring leak. Use downspout extensions to send water at least 2 m (6 ft.) away from the foundation, onto an area with good drainage such as a lawn or garden, and away from neighbouring houses too (Canada.ca: Eavestroughs and downspouts).
If your downspouts go into a pipe in the ground, check with your municipality before you change anything. Some cities require disconnection, and some require a permit or an exemption.
Extend the sump pump discharge
The federal sump pump guidance says the discharge pipe should empty at least 1.5 m (5 ft.) from your foundation if possible, onto an area with good drainage (Canada.ca: Sump pumps). The Intact Centre and the City of Toronto use 2 m. Going farther is better: water that drains back toward the house just gets pumped out again.
Seal and cover window wells
Look for cracks and gaps around basement window frames, remove the old caulking, and seal them with an exterior caulking that is weather-resistant and sticks to concrete (Canada.ca: Basement window maintenance). The Intact Centre recommends window wells that sit 10 to 15 cm (4 to 6 in.) above the ground and are sealed to the foundation, plus window well covers where fire escape requirements permit. A window that serves as a bedroom exit must stay usable as an exit, so pick a cover that opens easily from inside.
Add a water alarm
A battery water alarm near the sump pit or problem wall warns you before a small leak becomes a ruined floor.
Step 4: Bigger fixes (contractor work, over $250)
If the outside water is under control and you still get water in, it’s time for bigger work. The Intact Centre lists these as “complex upgrades” done with a contractor, for over $250. We don’t list prices for them because they depend heavily on the home, the soil and access. Get at least two written quotes.
Regrade the yard
Over time, soil settles beside the foundation and the ground ends up sloping toward the house. The Government of Canada says a 5% slope is ideal, a 2% grade is often considered the minimum, and the soil beside the foundation should be about 8 cm (3 in.) higher than the soil 1.5 m (5 ft.) away (Canada.ca: Property grading). Paved areas may need a different slope. Small low spots are a DIY job with topsoil and a rake; keep the soil below your siding and don’t bury the top of the foundation.
Seal foundation cracks
A single crack that leaks during spring melt can often be sealed. Canada.ca suggests caulking or hydraulic cement for hairline cracks and epoxy filler injection for larger ones under 0.5 cm (about 1/4 in.) wide, and recommends a professional for cracks that keep growing, large networks of cracks, or cracks where water seeps through (Canada.ca: Foundation maintenance). Fix the outside drainage first. A sealed crack with water still sitting behind it often leaks again somewhere else. Our guide to foundation cracks explains which ones are normal and which need an engineer.
Install or upgrade a sump pump and backup
If your home has a high water table or foundation drains that can’t drain properly, a sump pump moves water from the weeping tile out of the house. The federal guidance strongly recommends working with a licensed plumbing professional to decide whether you need one and to install it, recommends a backup pump with its own power source, and says sump pumps should generally be replaced about every 10 years, depending on the manufacturer (Canada.ca: Sump pumps). A licensed electrician may be needed for a dedicated circuit.
Install a backwater valve
If water comes up through the floor drain during heavy rain, the problem is likely a sewer backup, not a foundation leak. A backwater valve closes the sewer line when the sewer backs up. In Toronto it requires a building permit and an inspection before the valve is covered up, and while the valve is closed you should not use toilets, sinks or appliances because water won’t drain (City of Toronto). Hire a licensed plumber.
Exterior or interior waterproofing
When water keeps coming through the walls despite good drainage, the long-term options are exterior waterproofing (excavating and adding membrane and drainage outside the wall) or interior drainage to a sump. Both are major jobs. Ask any contractor what is causing the water, what the warranty covers and whether a permit is required.
Toronto subsidies (and checking for yours)
As of May 1, 2026, the City of Toronto’s Basement Flooding Protection Subsidy Program offers up to $6,650 per property for eligible work completed on or after November 12, 2025 (City of Toronto). Each subsidy covers up to 80% of the invoiced cost, to these maximums:
| Eligible work | Maximum subsidy |
|---|---|
| Home plumbing assessment (one-time) | $500 |
| Backwater valve and alarm | $1,600 per device, up to two devices |
| Sump pump and alarm | $2,250, one device |
| Sump pump battery backup | $300 |
| Foundation drain (weeping tile) severance and capping | $400 |
Conditions include: a single-family to fourplex home in Toronto, downspouts disconnected from the sewer (or exempted), contractors with a valid City of Toronto business licence, and an application within two years of the work. Funding is first-come, first-served.
Outside Toronto, many Ontario municipalities run their own programs. The Intact Centre’s checklist recommends checking with your municipality about basement flood protection subsidies and asking your insurer about discounts for flood-risk reduction (Intact Centre: Basement Flood Protection Checklist).
New home? Check your Tarion warranty
In Ontario, Tarion’s two-year warranty covers water penetration through the basement or foundation walls (actual leakage, not dampness or condensation). Call your builder before hiring anyone (Tarion).
Safety note
- Never step into a flooded basement if the water may reach outlets, cords or appliances. Shut off power at the panel only if you can reach it while standing on a dry floor; otherwise call your utility or an electrician.
- Sewer backup water is contaminated. Wear gloves and boots, and keep children and pets away.
- Use a partner when working on ladders.
- Call before you dig. In Ontario, request a free locate through Ontario One Call before regrading or digging near the foundation.
- Rules on downspouts, backwater valves and sump discharge vary by municipality. Check local bylaws and permit requirements before you start.
FAQ
Why does my basement only leak in spring?
Spring combines melting snow, frozen ground that can’t absorb water, and rain. Water collects against the foundation, especially where snow was piled. If it only happens in spring, start with snow clearing, downspouts and grading.
How far should downspouts discharge from the house?
At least 2 m (6 ft.) from the foundation, onto ground that drains well, according to Government of Canada and Intact Centre guidance.
Will home insurance cover a leaking basement?
It depends on the cause and your policy. Sewer backup and overland flooding are often separate coverages. Call your insurer and ask which apply to you.
The bottom line
Work from the outside in, and from cheap to expensive. Move snow away, extend downspouts, clear window wells and fix the grading before you spend money on a crack injection or a waterproofing contract. If water still comes in, or it comes up through the floor drain, bring in a licensed plumber or a foundation professional. Before winter, also read how to prevent frozen pipes.
This article is general information, not professional advice. See our Disclaimer.