A slab leak is a leak in a water line that runs under or inside a home's concrete foundation. Water escapes into the soil and slab, then seeps up into flooring and walls. Common signs are a warm spot on the floor, damp carpet or baseboards, the sound of running water and a high water bill. A plumber locates it with acoustic and thermal tools.
Key takeaways
- Slab leaks are common in Arizona because of hard water, soil movement and slab-on-grade homes.
- A warm floor usually means a hot water line is leaking.
- Repair options are a spot repair, a reroute through walls or attic, or pipe lining.
- Drying the slab and flooring is a separate job from fixing the pipe.
What is a slab leak?
Most homes in Apache Junction and the East Valley are built slab-on-grade. There is no basement or crawl space. The concrete foundation sits directly on the ground, and many water lines run beneath it or are cast into it. When one of those lines develops a hole, the water has nowhere visible to go. It saturates the soil and concrete, then wicks up into whatever sits on top.
Because nobody can see under the slab, these leaks often run for weeks before anyone notices. By then, flooring, baseboards and the bottoms of walls can be wet across a whole room or hallway.
What does a slab leak look like?
| Sign | Why it happens |
|---|---|
| Warm or hot spot on tile or concrete | A hot water line is leaking under that spot |
| Damp carpet or a wet baseboard with no clear source | Water is rising through the slab |
| Cracked, loose or hollow-sounding tile | Moisture and soil movement under the slab |
| Sound of running water with everything off | Water is escaping under pressure |
| Water meter moving when no water is in use | Water is leaving the system somewhere |
| Sudden jump in the water bill | A steady, hidden leak running day and night |
| Musty smell or mold near the floor | Long-term moisture under flooring |
| Water heater running more than usual | Hot water is constantly being replaced |
What causes slab leaks in Arizona?
Several local conditions work together:
- Hard water. Minerals in East Valley water pit copper lines from the inside over 15 to 30 years. Read more about pinhole leaks in copper pipes.
- Expansive soil. Clay and caliche swell after monsoon rain and shrink in drought, moving the ground under the slab.
- Heat cycles. Hot water lines expand and contract every day, and pipes rub against concrete or gravel.
- Construction issues. Kinked lines, poor bedding material or pipes touching rebar can wear through.
- High water pressure. Pressure that is too high stresses every joint in the system.
How do you find a slab leak?
Start with a meter test. Turn off every fixture and irrigation, then watch the leak indicator on your water meter. If it moves, close the main valve at the house. If it stops, the leak is inside the home's plumbing, possibly under the slab.
A leak detection plumber then narrows it down without tearing up floors:
- Line isolation and pressure testing shows whether the hot or cold side is leaking.
- Acoustic listening equipment picks up the sound of pressurized water escaping through concrete.
- Thermal imaging shows warm patterns from hot water leaks on the floor surface.
The goal is to mark the leak within a small area, so only a small section of floor is opened.
Warm floor or wet baseboards? Get leak detection and drying coordinated with one call.
Call: (856) 481-6893How do you fix a slab leak?
| Repair method | How it works | Best for |
|---|---|---|
| Spot repair | Open the floor and slab at the leak, repair the pipe, patch concrete and flooring. | A single leak in an otherwise sound system |
| Reroute | Run a new line through walls or the attic and abandon the old one under the slab. | Homes with repeat leaks or aging copper |
| Pipe lining | Coat the inside of the existing pipe with epoxy to seal small leaks. | Some cases, depending on pipe condition |
If your home has had more than one slab leak, ask about a reroute. Patching one leak in old copper often means another leak later.
How long does it take to fix a slab leak?
Detection and a spot repair often take a day or two. A full reroute can take a few days, depending on the size of the home. Drying is separate. Concrete releases moisture slowly, so drying the slab and the flooring above it often takes several days to a week or more. Our restoration process guide explains what happens during that time.
How much does slab leak repair cost?
The total depends on three things: how hard the leak is to reach, which repair method you choose, and how much water damage it caused. A spot repair under tile adds concrete and flooring work. A reroute adds wall patching. The longer the leak ran, the more flooring, baseboards and drywall need to be dried or replaced.
Coverage varies a lot. Many homeowners policies pay for sudden water damage and for access to the pipe, but not for the pipe repair. A slow leak may be denied. See whether a slab leak is covered by insurance or a home warranty, and report a slab leak the day you find it.