How to Detect a Water Leak in a Concrete Slab

Written by elle di jensen
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How to Detect a Water Leak in a Concrete Slab
A slab leak can cause a sudden increase in your water bill. (Push/Photodisc/Getty Images)

You might not think something as harmless as water could cause much damage to something as strong as concrete. A water leak, however, can be the trigger for serious problems in a concrete slab. If water leaks and pools under the concrete, it can make the soil uneven. This causes voids and hollows which can eventually cause cracks on the surface. And if you're in a freeze-thaw area ice can make your slab crack and buckle, causing an uneven surface. Detecting a water leak in or around a concrete slab is fairly simple and catching them early will prevent future problems.

Skill level:
Moderately Easy


  1. 1

    Examine the surface of the slab. Concrete is a porous material and any darkened spots that appear wet when there hasn't been any rain or snow (or if the slab is inside the home) indicate that water is seeping up from below the surface.

  2. 2

    Review your water and power bills and compare them to previous months. If there is a sudden increase it may be due to a water leak.

  3. 3

    Inspect the lower edge of the slab if it is on a hill or an incline. If water is leaking it will run downhill and pool at the lower edge of the slab.

  4. 4

    Check sprinkler lines that run near or under the concrete slab regularly for breakage or leaks. Routine checks of sprinklers will assure you catch leaks early enough to prevent damage to the concrete.

  5. 5

    Inspect the slab for signs of settling. If the slab has shifted or dropped it is possible there is a slab leak, especially if the ground was well compacted prior to pouring the cement.

Tips and warnings

  • If the main line supplying your home with water runs beneath your driveway, walkway or other concrete surface it may be the culprit of a leak. You can determine exactly where beneath your concrete the line runs by locating the main water line within your house and locating the water main outside the house (typically near the street). Run a sting line between the two points and mark it with spray paint. Pinpointing the location of the line may save you from having to break out and replace all of your concrete.

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