How to Tell If You Have a Leak Under Your Slab

Florida houses sit on concrete, and the water lines run underneath it. When one starts leaking, the house tells you in small ways before it tells you in expensive ways.

Almost every house in this part of Florida is built slab-on-grade. No basement, no crawlspace, just a poured concrete slab sitting on compacted fill with the house built on top. It is the right way to build here given our water table, and it works well.

The consequence is that the water supply lines feeding your fixtures run under that concrete. When one of them develops a leak, you cannot see it, you cannot get to it, and it can run for months pushing water into the ground beneath your house before anything obvious happens.

That is why knowing the early signs is worth something. A slab leak found in month one and a slab leak found in month eight are different repairs and very different conversations.

The sign that catches almost everyone first

A water bill that jumps with no change in how you live. Nobody moved in, nobody filled a pool, the irrigation schedule is the same, and the bill is suddenly noticeably higher. That is water going somewhere, and if it is not going anywhere you can see, it is going somewhere you cannot.

There is a check you can run yourself in about two hours. Turn off every fixture and every water-using appliance in the house. Go out to the meter and look at the low-flow indicator, which is usually a small triangle or dial that spins on even tiny flow. If it is moving with everything off, water is leaving the system somewhere. Read the meter, wait two hours with nothing running, and read it again.

With every fixture in the house shut off, the meter should be perfectly still. If it moves at all, something is leaking.

The rest of what the house tells you

• A warm spot on a tile or concrete floor, sometimes noticeable barefoot before it is noticeable any other way. That is a hot water line leaking underneath and heating the slab above it.
• The sound of water running when nothing is on. Usually a faint hiss or a rushing sound, often clearest at night when the house is quiet.
• Carpet that is damp in one area with no explanation, or a musty smell in one room that will not go away.
• Water pressure that has dropped noticeably throughout the house rather than at a single fixture.
• Cracks appearing in tile, in drywall, or across the slab itself, or doors that suddenly stick in their frames.
• Standing water or unusually green grass along the foundation line outside when it has not rained.
• A water heater running more than it used to, if the leak is on the hot side.

That warm floor spot is worth dwelling on because it is the most specific sign on the list. Concrete conducts heat well. A hot water line leaking under the slab heats the concrete above it, and that heat shows up as a patch of floor that is warmer than the floor around it. If you find one, you have effectively found the general area of the leak with your feet.

Why we do not just start looking

Here is the part that homeowners are most surprised by. Finding a slab leak is not a matter of poking around until you find it. Under the slab there is nothing to look at. The pipe is encased in concrete and buried in fill, and the water that escapes travels along the path of least resistance, which is often a considerable distance from where the pipe actually failed.

So the work is locating, and locating is done electronically. Acoustic listening equipment picks up the specific frequency signature that pressurized water makes escaping through a small opening in a pipe, and amplifies it through the concrete. Moving a sensor across the floor in a grid, the sound gets louder as you approach the source and quieter as you pass it, which pinpoints the spot. Thermal imaging maps temperature differences across the slab surface, which is how a hot line leak gets narrowed down fast.

The difference between locating a leak and guessing at one is the difference between a small opening in your floor and several.

What is actually corroding down there

Copper is the traditional under-slab supply material and it is durable, but it is not permanent in every soil. Soil chemistry varies enough around here that a line performing fine at one house can be under attack at the house down the road, and the sandy soils along the coast behave differently from the clay-heavier ground further north around DeFuniak Springs and Ponce de Leon.

Beyond soil chemistry, there is mechanical wear. Copper expands when hot water flows through it and contracts when it cools. Over decades of that cycling, a pipe rubbing against the concrete or against a piece of aggregate wears a thin spot, and the thin spot eventually opens. That is why hot water lines fail under slabs more often than cold ones, and why the warm floor spot is such a common first symptom.

There is also water velocity. A line that was undersized for its fixture load, or a house running high incoming pressure, moves water fast enough to erode the inside of a fitting from within. That kind of failure tends to show up at elbows, where the water changes direction.

The repair fork: through the slab or over the top

Once the leak is located, there are two real options and they suit different situations.

A spot repair means opening the floor directly over the leak, cutting out the failed section, and splicing in new pipe. It is the least disruptive to the rest of the house and the smallest job when the leak is in an accessible spot and the rest of the plumbing has life left in it. The tradeoff is that you have opened your floor covering, and if the same line fails again elsewhere, you are doing it again somewhere else.

A reroute abandons the under-slab section entirely and runs a new line overhead through the attic and down the walls to the fixtures. Nothing gets cut into the slab. The new line is accessible forever, which means the next repair on it, whenever that is, is a normal repair. The tradeoff is drywall work where the line drops down, and it is a bigger job up front.

Which one is right depends on the age and condition of the rest of the system, how many leaks that house has already had, and what the floor covering is. A first leak in a house with otherwise healthy plumbing is usually a spot repair. A second or third leak in the same house is telling you something about the whole under-slab system, and at that point continuing to spot repair is buying the same problem repeatedly.

You get the readings before you get an opinion

We locate first and talk second. When we tell you where the leak is, we can show you how we know, and when we lay out the two repair paths, we will tell you what each one takes rather than steering you toward the bigger one. Noah founded this company because he was tired of watching that go the other way.

We run leak locates across Freeport, Santa Rosa Beach, Miramar Beach, Destin, Niceville, Valparaiso, and the 30A towns. If your bill jumped or your floor has a warm spot, call 850-318-5777 and we will get it looked at.

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