Water coming through a basement wall: where it gets in and how to fix it

Do this first: make it safe and pin down where the water enters

1. Watch where the water first appears: a crack, a small tie hole in a poured wall, a mortar joint, around a pipe, under a window, or at the top of the wall.
2. Mark the wet area and the ends of any crack with a pencil and the date. Canada's flood guidance suggests marking crack ends to track changes in size or direction over time. ^[2]
3. Photograph the wall, the water and anything damaged before you clean up.
4. Move boxes, furniture and rugs away from the wall so it can dry.
5. Pick up water with a wet/dry shop vacuum once the power situation is safe. ^[3]
6. Start drying. EPA says that if wet materials are dried within 24 to 48 hours of a leak, in most cases mold will not grow. ^[4]
7. Go outside to the same spot and look at the gutter, downspout, soil slope and any window well above it.

If the water shows up only where the wall meets the floor, or rises through the floor, the page on water coming through the basement floor covers that joint, hydrostatic pressure and the condensation test. This page covers water coming through the face of the wall.

Where is the water getting in?

Canada Mortgage and Housing Corporation's damp basement guide (2007, revised 2008) says water penetrates or leaks through cracks, seams or openings in the basement walls, causing wet spots on walls or standing water on the floor below. It lists defective gutters and downspouts, poor grading, slow-draining backfill, improperly drained window wells, blocked or missing footing drains, a high water table and melting snow against the wall as likely causes. ^[5]

Table sources: CMHC's damp basement guide ^[5], CMHC's Mold in Housing guide ^[6], an ASHI Reporter article from 2007 ^[7] and an InterNACHI homeowner guide, which notes clogged gutters can overflow and send water down the inside of a wall. ^[8] CMHC's damp basement guide also lists clearing wall weep holes so rain does not drain to the top of the basement walls. ^[5] A 2018 University of Missouri Extension article adds that areas where walls meet are most susceptible to seepage, and to feel around basement windows for moisture. ^[9]

Cracks and leaks do not always go together. The 2007 ASHI article notes that a dry basement may have serious cracks while a leaky basement may be structurally sound, and that wet soil from poor surface drainage causes leaks. ^[7]

Test it before you pay for a fix

1. Wait for a dry day, then run a garden hose along the outside of the wall near the leak for a couple of hours, as CMHC's guide suggests, to confirm where the water enters. ^[5]
2. Move the hose a few feet at a time: first near the soil line, then into the window well, then at the downspout. The spot that makes the inside wet is your entry point.
3. Look for efflorescence, the white deposit CMHC describes as salts left behind when moisture dries toward the inside. CMHC lists efflorescence near a crack as one of its checks. ^[5]
4. Check whether the wall leaks right under low spots in the soil, downspout outlets or places where a patio or driveway has settled toward the house. CMHC lists these as checks. ^[5]
5. For a crack, measure its width and check the pencil marks over the next weeks. A crack that keeps growing needs a professional. ^[2]

Poured concrete or block: why it matters

Poured concrete walls shrink and crack. ASHI says some vertical shrinkage cracks in poured concrete can be up to 1/8 inch wide. ^[7] Poured walls also have form ties, the metal ties that held the forms together while the concrete set. CMHC's 2011 Mold in Housing guide lists sealing snap-tie holes, along with wall and floor cracks, from the inside with a suitable epoxy sealant. ^[6]

Block walls are different. Most blocks used in basements have a hollow core, and ASHI says block walls have less strength than poured concrete against sideways pressure. ^[7] CMHC says block walls tend to crack along mortar lines and that backfill pushing from the side often causes long horizontal cracks, usually between the first and second course up from the slab. ^[5] Water can also collect inside the hollow cores. CMHC warns that sealing a block wall from the inside with paints or coatings only holds water in the cavity, where pressure builds until it comes out at a seam or further along the wall. ^[5]

When a crack is a structural question. ASHI says any wall movement over 1/2 inch signals a potentially serious problem, and that in a block wall a horizontal crack over 1/8 inch wide with horizontal wall movement of 1/2 inch or more needs to be addressed. ^[7] Canada's flood guidance treats cracks under about 1/4 inch (0.5 cm) as ones you can seal, and says to consult a professional for larger cracks, cracks that keep growing, a large network of cracks, and cracks where water is seeping through. ^[2] Natural Resources Canada advises professional help for an active crack, one that gets bigger or smaller. ^[10]

Fixes from the inside

Inside patches can stop light seepage for a while. The 2018 University of Missouri Extension article says temporary patches can give one to two years of protection, and warns that once you patch one crack, water will find another place to enter. ^[9]

• Hairline cracks: University of Missouri Extension says waterproof silicone-based caulk can give temporary relief and is most suited to hairline cracks, those a credit card will slide into. ^[9]
• Small cracks with water coming through: hydraulic cement can be applied even while water is leaking. ^[9] CMHC's method is to cut a trough along the crack, clean it, mix enough cement to fill it in one go, and fill from the bottom up. It warns the cement sets very quickly and is extremely caustic. Wear gloves and eye protection. ^[5]
• Cracks 1/4 inch or wider: University of Missouri Extension suggests a cementitious coating, which resists water pressure. ^[9]
• Injection: epoxy or polyurethane is injected into the crack under pressure and sets inside it. CMHC says this is generally done by waterproofing contractors. ^[5]
• Tie holes: CMHC's 2011 guide lists sealing snap-tie holes from the inside with a suitable epoxy sealant. ^[6]

The limit. CMHC says that if there is enough water pressure behind the wall, or the crack widens later, water will push past any plug you put in its way. ^[5] University of Minnesota Extension calls an interior membrane or coating a temporary solution that may move the water to another path. ^[11] That is why the outside matters more.

Fixes from the outside, and what they cost

CMHC's first step is to cut the amount of water reaching the wall: gutters and downspouts, grading, snow removal and window wells. ^[5] The heavy rain page covers gutters and downspouts in detail. For a wall leak, look hardest at these:

• Slope. CMHC's Mold in Housing guide says the finished grade should slope away from the foundation by at least 6 inches over 10 feet, with at least 8 inches of foundation showing above grade. ^[6] University of Minnesota Extension's figure is at least 1 inch per foot for at least 6 feet. ^[11]
• Downspouts. University of Missouri Extension says flexible extenders can carry water 10 feet out and downhill from the house. ^[9] University of Minnesota Extension's minimum is at least 4 feet beyond the wall. ^[11]
• Window wells. CMHC says the top of the well should sit well above grade, be fastened and sealed to the wall, and drain at the bottom to the perimeter tile, with at least 200 mm, about 8 inches, between the bottom of the window and the floor of the well. Otherwise water may collect and leak in through or around the window. ^[6]
• Pipe and wire openings. Canada's flood guidance says to make sure seals around windows, doors, vents and pipes set in the foundation are water-tight, and to remove old caulk before replacing it. ^[2]
• Excavation. Natural Resources Canada says persistent leaks often need excavating, damp-proofing or waterproofing, and a drainage system. ^[10] University of Minnesota Extension calls exterior drainage the most costly but most effective approach. ^[11]

Cost. Angi's basement waterproofing guide, updated July 20, 2026, says minor basement leaks cost around $250 to repair, and extensive leaks or a series of leaking areas up to around $10,000. Sealing foundation cracks can cost as little as $600, interior waterproofing averages about $3,000 and extensive exterior work about $7,000. Most waterproofing jobs run $2,461 to $8,205, with an average of $5,244. Basement size, method, clay soil, a high water table, and block versus poured walls move the price. ^[12]

Insurance rarely helps with the leak itself. Washington's insurance commissioner says homeowner insurance usually does not cover water damage from a leaking foundation or cracks in walls. ^[13] Wisconsin's regulator says seepage through the foundation is not covered by a standard homeowners policy. ^[14] Check your own policy.

When to call a pro, and which one

Three different trades handle this. A waterproofing or drainage contractor stops water from getting in. A structural engineer judges cracks and moving walls. A water damage restoration company deals with water already inside.

• Structural engineer or foundation professional: a horizontal crack, a bowing wall, movement over 1/2 inch, or a crack that keeps growing. ASHI and Canada's guidance point these to a professional. ^{[7] [2]}
• Waterproofing contractor: water keeps coming after you fix gutters, grading and window wells, or you want cracks injected.
• Restoration company: drywall, framing, carpet or insulation in a finished basement got wet. Massachusetts guidance says to cut out wallboard that has not dried within 48 hours. ^[15]
• Restoration company: water is spreading across the floor or is near outlets, cords or the panel.
• Any of them: you suspect a leak but cannot find the source. Canada's flood guidance says there could be damage you cannot see without professional inspection or excavation. ^[2]

Common questions