Search guides

How to fix a basement leak

We'll locate the source, improve drainage, seal small cracks, and tell you when to call a professional.

How-to · Home plumbing
1–4 hours
What you'll need
  • Hydraulic cement or epoxy injection (for small cracks)
  • Downspout extensions
  • Wire brush, flashlight
  • Window well cover (if needed)

At a glance

  • Locate where water enters—foundation cracks, window wells, sump pump, or at the floor-wall joint.
  • Check gutters and downspouts; extend them at least 4 feet from the foundation.
  • Seal small foundation cracks with hydraulic cement or epoxy injection.
  • Improve grading so water slopes away from the foundation.
  • Call a plumber or waterproofing professional for large cracks, structural issues, or persistent flooding.
Quick triage — pick your path

Get started

Choose the option that matches what you see. You can jump straight to that section.

Steps

Goal: Locate the source, improve drainage, seal small cracks, and know when to call a professional.

  • During or after rain, watch where water appears in the basement. Trace the path with a flashlight.
  • Good: You identify the source—foundation crack, window well, sump pump, or floor-wall joint. Proceed to Check gutters or Seal cracks based on the source.
  • Bad: Cannot locate the source—call a professional.

Check gutters

Goal: Redirect water away from the foundation.

  • Inspect gutters for clogs. Confirm downspouts extend at least 4 feet from the foundation. Add downspout extensions if they dump water next to the foundation. Improve grading so the ground slopes away from the house—at least 6 inches over 10 feet.
  • Good: Water flows away from the foundation. Proceed to Verification.
  • Bad: Gutters and grading are correct but the basement still leaks—check Seal cracks or Fix window well.

Seal cracks

Goal: Seal small foundation cracks to stop water entry.

  • For small cracks (less than 1/4 inch wide), clean the crack with a wire brush. Apply hydraulic cement or epoxy injection per the product instructions. For cracks that are actively leaking, use a product designed for wet cracks.
  • Good: The crack is sealed and no water enters. Proceed to Verification.
  • Bad: The crack is large or widening—do not seal. Call a professional.

Fix window well

Goal: Stop water entering through window wells.

  • Check that the window well has a drain at the bottom and that it is not clogged. Add a window well cover to keep rain out. If the well fills with water, clear the drain or install a new drain.
  • Good: No water pooling in the window well. Proceed to Verification.
  • Bad: Drain is blocked and you cannot clear it—call a professional.

When to get help

Call a plumber or waterproofing professional if:

  • The crack is large or widening.
  • You see structural damage.
  • Water is flooding the basement.
  • The sump pump has failed and you cannot fix it.
  • You have tried drainage improvements and the leak persists.

Do not seal large cracks yourself—you can mask a serious problem.

Verification

  • No water entering the basement during or after rain.
  • Gutters and downspouts direct water away from the foundation.
  • Small cracks are sealed. The sump pump runs when the pit fills.

Reviewed by Blackbox Atlas

Frequently asked questions

Why does my basement leak?
Common causes: foundation cracks, poor drainage (gutters, grading), window well leaks, or a failed sump pump. Water pools against the foundation when gutters are clogged or downspouts are short; hydrostatic pressure forces water through cracks.
Can I fix a basement leak myself?
Yes, for small cracks and drainage improvements. Seal small cracks with hydraulic cement. Extend downspouts and improve grading. If the crack is large, the foundation is shifting, or water is flooding, call a waterproofing professional.
When should I call a plumber for a basement leak?
Call a plumber or waterproofing professional if the crack is large or widening, you see structural damage, water is flooding, or the sump pump has failed. Do not attempt to seal large cracks or structural issues yourself—you can mask a serious problem.

Rate this guide

Was this helpful?

Continue to