Note to readers: This post was updated on July 19, 2026 to expand on slab leak causes, add earthquake-related context, and link to our leak detection service and safety guides. We refreshed the details below so the advice reflects how we approach this work today.
A slab leak is a broken water line running beneath the concrete foundation of your home. It’s one of the more stressful plumbing problems homeowners face, mainly because the damage happens where you can’t see it — often for weeks before it becomes obvious.
What Causes a Slab Leak?
Several things can lead to a pipe failure under a concrete slab:
- Ground and foundation shifts. As soil settles or shifts, it puts pressure on the pipes running through or under the slab.
- Earthquakes. Southern California sees regular seismic activity, and even minor shaking can stress pipe joints over time. See our guide on earthquake shut-off valves for related seismic safety info.
- Pipe abrasion. Pipes naturally expand and contract as water flows through them. When they sit close to concrete, gravel, or other pipes, that movement causes friction, which wears through the pipe wall over years.
- Corrosion. Repeated contact with soil and moisture corrodes metal pipe over time, especially in older homes with galvanized or copper lines.
Warning Signs of a Slab Leak
Slab leaks rarely announce themselves clearly. Watch for:
- A water bill that jumps with no change in usage
- A hot spot on your floor (a sign the leak is on the hot water line)
- The sound of running or hissing water when nothing is turned on
- A water meter dial that keeps moving when all fixtures are off
- Low water pressure throughout the house
- Cracks in baseboards, walls, or flooring
- Damp, warm, or musty-smelling floors
Why You Shouldn’t Wait
Left unaddressed, a slab leak can undermine your foundation, warp flooring, and cause mold growth inside walls. What starts as a plumbing repair can turn into a much larger and more expensive foundation or flooring job the longer it runs unnoticed.
How Slab Leaks Get Fixed
The repair approach depends on where the leak is and how bad the damage is. Options range from spot repair (accessing just the damaged section of pipe) to rerouting the line above the slab to avoid digging into concrete altogether. A professional leak detection visit will pinpoint the exact location before any concrete gets touched, which keeps the repair as targeted (and affordable) as possible.
If you’re noticing any of the warning signs above, don’t wait for it to get worse. Contact Western Rooter for a free visual estimate — leak detection service starts affordably, and catching a slab leak early is almost always cheaper than the alternative.
