A slab leak is a pipe leaking under your foundation — hidden, but destructive. Warm spots on the floor, a spiking water bill, the sound of running water with everything off. Here’s how we find and fix it.
Written bySteven Lockhart·Reviewed byMiguel Lopez, Owner & Licensed Plumber, New Pro Plumbing (CSLB #974600)·Last reviewedAugust 2026 · 7 min readQuick Answer
A slab leak is a water line leaking beneath your home’s concrete foundation. Signs include unexplained warm spots on the floor, a sudden jump in your water bill, low pressure, and the sound of running water when everything is off. New Pro uses electronic leak detection to pinpoint slab leaks and repair them with minimal disruption, 24/7.
A slab leak happens when a water line running beneath your home’s concrete slab foundation springs a leak. Because it’s hidden under the concrete, it can run for a long time before you notice — quietly driving up your water bill, warming the floor above a hot-water line, and saturating the ground under your home.
Slab leak repair — Slab leak repair is the detection and repair of a water line leaking beneath a home’s concrete foundation, typically pinpointed with electronic equipment and fixed by spot repair, rerouting, or repiping.
It’s one of the more serious calls an emergency plumber gets, because the damage compounds: left alone, a slab leak can erode soil under the foundation and invite mold.
A slab leak seeps; a burst pipe floods fast — the response differs.
Electronic acoustic and pressure equipment pinpoints the leak so we open concrete only where needed.
Detect precisely, then choose the least-invasive repair.
We verify a slab leak versus another source with a pressure test.
Acoustic and pressure tools pinpoint the leak’s location.
We locate it from the surface to minimize concrete opening.
Spot repair, reroute the line, or repipe — based on the pipe.
We fix the line and confirm the leak is gone.
We close up and leave the area clean.
Warm floor and a high bill? Those are classic slab-leak signs. If instead water is dripping from above, see ceiling water leaks; if it’s under a cabinet, see under-sink leaks.
Hearing running water with everything off? That’s worth a call today.
Get a Free QuoteThe danger of a slab leak is precisely that it’s silent. Unlike a burst pipe that announces itself with a flood, a slab leak can seep under your foundation for weeks or months, and the first real clue is often a water bill that’s quietly climbed or a patch of floor that’s warm underfoot. By the time the signs are obvious, the leak has usually been running a while — which is why acting on the early hints, rather than waiting for certainty, saves both water and foundation.
The stakes are higher than the water itself. Constant moisture under a slab can erode the supporting soil and lead to foundation movement, and it creates the damp conditions mold needs to take hold. Those are far more expensive problems than the plumbing repair that would have prevented them. The U.S. EPA’s WaterSense program notes that household leaks waste huge volumes of water nationwide, and a slab leak — running continuously and invisibly — is among the worst offenders a home can have.
Because slab work touches the foundation, it’s not a place for guesswork or unlicensed shortcuts. We detect electronically before opening anything, work under a license you can verify with the CSLB (#974600), and permit the repair through the Los Angeles Department of Building & Safety where required. That discipline protects your home and gives you documented work for insurance and resale.
The right fix depends on the pipe’s age and how many leaks it has.
| Situation | Method | Concrete work |
|---|---|---|
| Single isolated leak | Spot repair | Minimal opening |
| Aging / repeat leaks | Reroute line | Often avoids the slab |
| Failing whole line | Repipe | Varies |
We’ll walk you through each option and its price — clear, flat-rate, the way 24/7 emergency plumbing should be.
Slab leak cost depends on the detection, the repair method, and how accessible the leak is. Detection is the first, essential step — it’s what lets us avoid jackhammering more concrete than necessary. A simple spot repair costs less than a reroute or repipe. After detection, you get one flat-rate price for the fix.
Even on an urgent call, we quote before we cut — see how our emergency plumbing service handles flat-rate pricing.
A homeowner notices a warm patch on the floor and a water bill that doubled with no change in usage.
New Pro pressure-tests the system, pinpoints a hot-water slab leak electronically, and reroutes the short affected run.
The leak's fixed with a minimal opening, the bill returns to normal, and the foundation is protected before damage set in.
The Bottom Line
A slab leak is sneaky and destructive, but it’s very fixable — the key is finding it precisely before touching concrete. If your floor has a warm spot, your bill jumped, or you hear water with everything off, don’t wait for the foundation to suffer. Detection first, then the least-invasive repair.
The classic signs are an unexplained spike in your water bill, warm or hot spots on the floor from a leaking hot-water line, low water pressure, the sound of running water when every fixture is off, and sometimes cracks in flooring or walls or a damp, musty smell. Any one of these is worth investigating; together they strongly suggest a leak under the slab that needs prompt attention before it damages the foundation.
We use electronic leak detection — acoustic listening equipment that hears the leak through the slab, combined with pressure testing to confirm which line is leaking. This pinpoints the leak’s location precisely from the surface, so when a repair does require opening concrete, we open only the small area directly over the leak rather than exploring blindly. Detecting first is what keeps the repair minimally invasive.
Serious enough to address promptly. Beyond wasting water and inflating your bill, a slab leak saturates the soil under your foundation, which over time can cause the foundation to shift, settle, or crack. The constant moisture also invites mold. It won’t fix itself and tends to worsen, so while it’s not a flood-in-minutes emergency like a burst pipe, it’s not something to leave for later either.
Often, yes. If it’s a single, isolated leak in an otherwise sound line, a spot repair or a short reroute of the affected section may be all that’s needed. Repiping is reserved for older lines that have leaked repeatedly or are likely to keep failing. We assess the pipe’s age and history and recommend the least-invasive option that will actually last, rather than defaulting to the biggest job.
Common causes include corrosion of copper or galvanized lines over time, abrasion where a pipe rubs against the concrete or rebar as it expands and contracts, poor initial installation, and high water pressure stressing the lines. Older homes and homes with hard water are more prone to them. Because the cause is usually related to the pipe’s age or condition, a slab leak sometimes signals that the wider line is nearing the end of its life.
Written by the New Pro Plumbing content team and reviewed for technical accuracy by Miguel Lopez, owner and California-licensed plumber (CSLB #974600). Guidance follows U.S. EPA, CSLB, and LADBS sources where cited. Any figures reflect New Pro Plumbing's flat-rate practice and West LA conditions, not a quote — we confirm pricing in writing before any work begins.
Last reviewed: August 2026.
Honest diagnosis, flat-rate price agreed first, and a clean, code-compliant fix from a family-owned Westside plumber.
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