Under-Slab Leak Detection

Signs the leak is under the slab specifically

• A warm or hot spot on the floor itself, not the wall (a hot-water line under the slab)
• The sound of running water through the floor when every fixture is off
• A water meter that keeps moving with the whole house shut off
• Tile cracking, grout lines separating, or wood flooring buckling in one localized area
• Reduced hot water pressure with no other cause found upstream

How professionals confirm and locate an under-slab leak

Detection starts by isolating the system: shutting the main and watching the meter, then separating hot and cold lines to determine which side is losing water. From there, acoustic listening equipment reads the sound of escaping water through the concrete, thermal imaging maps warm-water lines, and pressurized tracer gas pinpoints the break to a small, specific area of slab.

Because the target is buried in structural concrete, accuracy matters more here than for any other kind of leak — it determines whether the repair is a small spot cut through the slab, an overhead or through-wall reroute that avoids the concrete entirely, or a partial repipe.

What a licensed pro checks before recommending a repair method

• Which line is affected — supply (pressurized, continuous loss) or drain (intermittent, tied to fixture use)
• Depth and routing of the slab plumbing relative to load-bearing areas
• Condition of the rest of the under-slab piping, since one failure on aging pipe often means others are close behind
• Whether rerouting overhead or through a wall avoids cutting the foundation at all

Is an under-slab leak an emergency?

It is urgent rather than instantly catastrophic. A slab leak rarely floods a home in minutes, but it can erode soil under the foundation, drive humidity and mold, and waste large volumes of water. Most homeowners should have it evaluated within days, not months.

South Florida specifics

Slab-on-grade construction is standard across South Florida, so nearly every home has plumbing running directly under the concrete rather than in a basement or crawlspace. A high water table in Miami-Dade and Broward means soil under a leaking slab saturates quickly, and older homes from the mid-20th century onward often have the original copper or cast iron under-slab lines nearing or past typical service life. Hard water accelerates pinhole corrosion in copper, which is one of the most common under-slab leak causes seen in the region.

Signs of a slab leak, strongest first

The meter test you can run yourself in ten minutes

1. Turn off every fixture and appliance that uses water, including ice makers and irrigation.
2. Find the water meter and note the reading and the position of the low-flow indicator.
3. Wait 30 to 60 minutes without using any water at all.
4. Read it again. Any movement means water is leaving the system somewhere.
5. To narrow supply-side versus house-side, close the main shut-off at the house and repeat: if movement stops, the loss is inside the home's plumbing.
6. Record both readings. The EPA's Fix a Leak Week guidance uses this same meter method, and a provider will want the numbers.

How professionals locate the leak without breaking the floor

The point of detection is to reduce the repair to a single known location. A provider who wants to open multiple sections of floor to find it has skipped the step you are paying for.

• Acoustic listening equipment amplifies the sound of pressurized water escaping through concrete and is the primary locating tool.
• Line tracing and pressure isolation confirm which line — hot, cold or a specific branch — is losing water.
• Thermal imaging highlights temperature differences from a hot-line leak spreading under the floor.
• Tracer gas is used when a leak is too quiet for acoustics, introducing a safe gas that surfaces at the leak point.
• Moisture meters map how far water has already tracked, which decides the drying scope separately from the repair.

Repair options once the leak is located

Repeat pinhole failures in the same run generally point to the condition of the pipe rather than to bad luck, which is what shifts the conversation from spot repair to reroute or repipe.

Why South Florida sees slab leaks

Most single-family housing here is slab-on-grade, so supply lines are cast into or beneath the concrete rather than running in a basement where a leak would be visible. Combine that with a high water table, mineral content in the supply, and copper installed in mid-century construction, and leaks tend to be discovered by their symptoms rather than by sight.

Because the slab hides the loss, the gap between when a slab leak starts and when it is noticed is often weeks — which is why drying and moisture mapping is normally part of the job, not an upsell.

How to check that a plumber for slab work is licensed and insured

• Ask for the license number and look it up yourself — Florida licenses are searchable through the DBPR portal, and slab repairs that alter the plumbing system may require a permit.
• Ask for a certificate of insurance naming general liability and workers' compensation coverage, issued by the insurer rather than the contractor.
• Get the scope in writing before work starts: what is being repaired, what is being replaced, what happens if the crew finds something worse once they open things up.
• Ask who pulls the permit when one is required, and confirm the inspection is included rather than left to you.
• Be cautious with anyone who will not put a diagnosis in writing, demands full payment up front in cash, or pressures you to decide before you have seen the scope.

How UrgentHomePro fits in

UrgentHomePro is a matching service, not a contractor. We do not perform work, employ technicians, set prices or guarantee an arrival time. When you submit a request or call, we route the details to independent local professionals who serve your ZIP code, and you agree scope and price directly with whoever contacts you.

We may be compensated by participating providers when a request is routed to them. That is why every cost section on this site explains what drives a price instead of quoting one — the only accurate number is the one a licensed provider gives you after seeing the job.