How to spot a slab leak

What a slab leak is

In homes built on a concrete slab, the water supply lines often run under or through the concrete. A slab leak is a leak in one of those buried pipes. Because you can't see the pipe, the first clues are usually indirect, and the leak can run for weeks before anyone notices.

Slab leaks happen when pipes wear against concrete or gravel, corrode, get pinched as the ground shifts, or were damaged when the house was built. Clay soils that swell when wet and shrink when dry, which are common in parts of Alabama, can add to that movement.

Signs of a slab leak

• A water bill that jumps without any change in how much water you use.
• The sound of running water when every faucet and appliance is off.
• Warm or hot spots on the floor, often felt barefoot. That points to a leak on a hot water line.
• Damp carpet, warped wood or lifting tile with no leak from above.
• Lower water pressure across the house.
• The water heater runs more than usual, because it keeps heating water that's leaking away.
• Mildew or a musty smell near the floor, or water seeping at the base of a wall.
• New cracks in the floor or walls, though cracks have many causes.

The water meter test

This simple test tells you whether water is leaking somewhere in the house.

1. Turn everything offMake sure no faucets, toilets, ice makers, irrigation or appliances are using water.
2. Find the meterIt's usually in a box near the street. Lift the lid carefully.
3. Look for movementMany meters have a small triangle or dial that spins when any water flows. If it's moving with everything off, water is leaking somewhere.
4. Or take two readingsWrite down the number, wait 30 to 60 minutes without using any water, then read it again. Any change means a leak.
5. Narrow it downClose the main shutoff valve at the house and check the meter again. If it still moves, the leak is probably in the line between the meter and the house. If it stops, the leak is inside the house, possibly under the slab.

How plumbers find the leak

Plumbers don't have to break up the floor to find a slab leak. Common methods include:

• Pressure testing each line to tell whether the leak is on the hot side or the cold side.
• Acoustic listening equipment that picks up the sound of water escaping through the concrete.
• Thermal imaging to spot warm areas from a hot water leak.

Good leak detection lets the plumber open the floor in one small spot, or skip it altogether.

Repair options

1. Spot repairThe plumber cuts a small opening in the slab right over the leak, fixes the pipe and patches the concrete. This makes sense for a single leak on otherwise sound pipe.
2. Rerouting the lineInstead of digging, the plumber abandons the leaking section and runs a new line through walls or the attic. This avoids breaking the floor and is often recommended if more leaks are likely.
3. RepipingIf the pipes are old and leaks keep happening, replacing the supply lines for the whole house can cost less in the long run than repeated spot repairs.

Ask the plumber why they recommend one option, how old they think the pipes are, and how likely another leak is.

Does insurance cover slab leaks?

It depends on your policy. Some policies cover the cost of finding the leak and repairing the damage it caused, like flooring, but not the pipe repair itself. Others exclude slow leaks. Call your insurer before the repair starts, and keep photos, the leak detection report and every receipt.

Questions people ask

This guide is general information for homeowners, not professional advice for your specific home. Plumbing Tuscaloosa is a referral service and does not do plumbing work; a licensed plumber should look at your situation before any repair.