Basement Leak Repair — Where the Water Is Coming From, and Who Fixes It

The repair depends entirely on the entry point. Find yours below, then see what it usually means, what fixes it, which trade does that work in Ontario, and whether a city rebate pays for any of it.

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Three ways water gets in

Infiltration — through cracks, the wall–floor joint, window wells and pipe penetrations. Groundwater.
Sewer backup — up through the floor drain, toilet or shower. The municipal sewer surcharged.
Overland — in through doors, windows and vents from water flowing across the surface.

They can happen together in one storm. Each needs a different fix, and only one of them — sewer backup — has a widely subsidised solution.

Find your entry point

Where the wall meets the floor

What it looks like: A damp line or puddle along the base of the wall after heavy rain or snowmelt; efflorescence (white powder) on the block.
What it usually means: Groundwater pressure at the footing. The weeping tile is overwhelmed, silted, or has no working outlet, so water rises through the cove joint.
The fix: Interior drainage channel at the joint feeding a sump pit and pump; or exterior excavation, membrane and new weeping tile for the complete fix.
Who does it: Waterproofing contractor for the drainage work; a licensed plumber connects the sump pump.
Rebate: The sump pump and its battery backup are eligible under Toronto’s program ($2,250 + $300); the drainage channel and membrane are not.

A crack in the foundation wall

What it looks like: Water tracks down from a visible crack — often a vertical or diagonal shrinkage crack in poured concrete, or an open mortar joint in block.
What it usually means: A non-structural crack that has become a water path. If the crack is displaced (one side proud of the other), widening, or horizontal, get a structural opinion before anyone seals it.
The fix: Epoxy or polyurethane injection from inside for a stable crack; exterior repair for a displaced or recurring one. Get a structural opinion first if it is moving.
Who does it: Foundation-repair or waterproofing contractor.
Rebate: No Ontario city program covers crack injection or wall repair.

A window well

What it looks like: Water pooling in the well, then entering at the sill or the frame; worst during downpours.
What it usually means: The well’s drain is clogged or missing, the ground slopes toward it, or it has no cover — so it fills like a bucket.
The fix: Clear or add the well drain (tied to the weeping tile), regrade around it, fit a cover. Replace a rotted frame.
Who does it: Waterproofing contractor or a general contractor; a cover is a homeowner job.
Rebate: Not covered by city programs.

The floor drain, a toilet or a shower

What it looks like: Water — often grey and foul — rising from the drain during a storm, sometimes hours after the rain stops.
What it usually means: Sewer backup. The municipal sewer surcharged and pushed flow back up your lateral into the lowest fixtures in the house.
The fix: A backwater valve on the sanitary lateral; disconnect downspouts and foundation drains from the sanitary sewer so your own roof water is not part of the surge.
Who does it: Licensed plumber or drain contractor (in Toronto: T94, T92, T87 or T85 licence classes). A building permit and inspection are usually required.
Rebate: Covered: Toronto pays 80% up to $1,600 per valve, and every one of the eleven other Ontario city programs we track has a backwater valve rebate.

Around a pipe, cable or the sewer line where it passes through the wall

What it looks like: A wet ring around a service entry, dripping onto the floor below it.
What it usually means: The seal around the penetration has failed; groundwater follows the pipe in.
The fix: Cut back and re-seal the penetration with a hydraulic cement and a flexible sealant, or an injected seal for a wet one.
Who does it: Waterproofing contractor; a plumber if the pipe itself is leaking.
Rebate: Not covered by city programs.

From above — after rain, not groundwater

What it looks like: Water on the floor near a downspout side of the house, or along a wall below a low spot in the yard.
What it usually means: Roof water is being delivered to the foundation: a downspout discharging at the wall, or grading that slopes toward the house.
The fix: Extend downspouts well away from the foundation, regrade so the ground falls away from the wall, keep window wells covered. In Toronto the Sewers By-law requires downspouts to be disconnected from the underground sewer connection.
Who does it: You, or a landscaper. This is the cheapest fix on the page and the one to do first.
Rebate: Some cities pay toward downspout disconnection (Halton, Hamilton, Mississauga); Toronto’s subsidy does not include it.

Do the outside first

Before anyone quotes an excavation, take the water away from the house. Extend every downspout so it discharges well clear of the foundation, make sure the ground falls away from the wall on every side, and cover the window wells. The Institute for Catastrophic Loss Reduction lists downspout disconnection, lot grading and window well covers as the first line of household protection because they reduce the water reaching the weeping tile in the first place. A surprising share of “leaks” stop here. If yours does not, the problem is below grade and the sections above apply.

What it costs — and what we will not guess

Two of the repairs on this page have verified Ontario price pages: backwater valve installation and sump pump installation, each with the net figure after the Toronto subsidy. Crack injection is priced per crack and waterproofing per linear foot of wall, and both vary with access and depth — we do not have a verified Ontario price series for them yet, so we are not going to print one. Get two itemised quotes and ask each contractor to name the entry point they are fixing.

What a city rebate covers — honestly

Ontario municipal programs fund flood-protection plumbing: the backwater valve, the sump pump and its battery backup, and in Halton, Markham and Mississauga the weeping-tile disconnection or capping that goes with a sump pump. Toronto’s program adds a plumbing assessment and foundation-drain capping. None of them pay for a membrane, an injection or a new window well. If your leak is groundwater at the cove joint and the fix includes a sump pump, that part may be subsidised. If it is a wall crack, it will not be. Every city program, with amounts.

Next step

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FAQ

Why does my basement leak only when it rains hard?

That pattern usually means infiltration: rain saturates the soil around the foundation, groundwater pressure rises, and water finds the weakest point — the wall–floor joint, a crack, or a window well. If the water instead comes up through a floor drain or a basement toilet during the same storms, that is sewer backup, which is a different problem with a different fix (a backwater valve).

Who should I call for a leaking basement — a plumber or a waterproofing company?

It depends on where the water enters. Water through the floor drain, a toilet or a shower during a storm is sewer backup — a licensed plumber or drain contractor installs the backwater valve. Water through the wall–floor joint, a crack in the wall or around a pipe penetration is infiltration — a waterproofing or foundation-repair contractor does that work, and a plumber connects the sump pump if one is part of the fix.

Will a city rebate pay for basement leak repair?

Ontario city programs pay for flood-protection plumbing — backwater valves, sump pumps (and battery backup), and in some cities weeping tile disconnection with a sump pump — not for waterproofing membranes or crack injection. Toronto’s program covers the backwater valve, the sump pump, its battery backup, foundation-drain capping and a plumbing assessment. If your leak needs a sump pump, that part may be subsidised; the crack injection or membrane will not be.

Can I fix a leaking basement from the inside?

Often, yes. An interior drainage channel at the wall–floor joint that feeds a sump pit, and epoxy or polyurethane injection for a non-structural crack, are both interior repairs. Exterior waterproofing (excavating to the footing and applying a membrane) is the more complete fix and the more expensive one. A contractor should tell you which applies and why — and if a crack is displaced or widening, get a structural opinion before anyone seals it.

What should I check before paying anyone?

The free things first: downspouts disconnected and extended away from the house, ground sloping away from the foundation, window wells clear of debris and covered. In Toronto the Sewers By-law requires downspouts to be disconnected from the underground sewer connection. If the leak persists after that, the problem is below grade and it is time to get two quotes.

Sources

Institute for Catastrophic Loss Reduction (ICLR) — Handbook for Reducing Basement Flooding (Dan Sandink). Handbook 2009; ICLR flood page and "Good / Better / Best" retrofit advice April 21, 2026. Used for: the three mechanisms of basement flooding (overland, infiltration, sewer backup); where infiltration enters; what each protective measure does.
City of Toronto — Basement Flooding Protection Subsidy Program. Page modified June 18, 2026 (re-read September 4 and 11, 2026). Used for: eligible sump pump work, 80% / per-item maximums, discharge to a permeable surface ≥ 2 m from the foundation, eligible licence types T94 / T92 / T87 / T85, photo requirement, two-year application window.
City of Toronto — Sewers By-law — Toronto Municipal Code, Chapter 681. Page modified July 23, 2026; Chapter 681 §681-11 (downspouts). Used for: downspouts must be disconnected from the underground sewer connection and roof water conducted away from the building (§681-11).
City of Toronto — Foundation Drainage Policy and Guidelines — FAQ. January 4, 2022 (policy effective January 1, 2022). Used for: foundation drain (weeping tile) connections to the sanitary sewer are strongly discouraged by the MECP; on-site management (sump, infiltration) is the expected approach.

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