9 Signs of a Slab Leak in Your Home

What is a slab leak?

A slab leak is a leak in a water line that runs under or through a home's concrete foundation. Nearly all East Valley homes are built on slabs, and hard water plus shifting desert soil wear on the pipes beneath them. Because the leak is out of sight, you usually notice its effects first.

9 signs of a slab leak

1. A warm or hot spot on the floor. A leaking hot water line heats the concrete above it. Bare feet often find it first.
2. The sound of running water when every faucet, toilet and appliance is off.
3. A higher water bill with no change in your usage.
4. A water meter that keeps moving when all water is off. See the test below.
5. Damp or wet carpet with no spill or visible source.
6. Warped, cupped or loose flooring, especially laminate, vinyl plank or wood.
7. Cracked or lifted tile or new cracks in the slab.
8. A musty smell or mold along baseboards and the bottom of walls.
9. Low water pressure or a water heater that runs constantly.

One sign alone can have other causes. Two or more together are a strong reason to call a plumber for leak detection.

How to do the water meter test

1. Turn off every faucet, shower, toilet, washer, dishwasher, ice maker and irrigation system.
2. Find your water meter, usually in a box near the curb.
3. Look at the leak indicator, a small triangle or dial that spins when any water flows.
4. If it moves with everything off, water is going somewhere.
5. To narrow it down, close the main shutoff at the house. If the meter stops, the leak is inside the house or under the slab. If it keeps moving, the leak is likely in the line between the meter and the house, or in irrigation.

Why slab leaks are common in the East Valley

• Hard water slowly corrodes copper from the inside.
• Expansive soil and caliche shift under the slab as they wet and dry.
• Hot water lines expand and contract with each use, which wears them faster.
• Pipe age. Homes built from the 1970s through the early 2000s are reaching the age when pinholes form.

What to do if you suspect a slab leak

1. Call a licensed plumber for electronic leak detection and repair.
2. Photograph the signs: wet flooring, the meter test, your water bills.
3. Call your insurer to ask about coverage for water damage and access to the pipe.
4. Call a restoration company to dry the slab and flooring once the leak is stopped.

Don't wait on a slab leak

Water from a slab leak keeps soaking flooring and walls every hour it runs. Hidden moisture along baseboards is a common start for mold. Our guide to signs of mold behind walls explains what to watch for.