Slab Leak Signs: What Florida Homeowners Should Watch For

What a slab leak actually is

Most houses in Lee, Charlotte and Collier Counties are built slab on grade. There’s no basement and usually no crawlspace, so the concrete pad poured at ground level is the floor of the house. In a lot of these homes, the water supply lines run under that slab or are set into it before the concrete goes down, then come up through the floor at fixtures, the water heater and the kitchen.

When one of those buried lines develops a pinhole, a cracked fitting or a full break, the water has nowhere obvious to go. It soaks into the fill and sand under the house, works its way along the path of least resistance and may not show up for weeks. That’s what makes slab leaks frustrating. You often notice the side effects long before you see any water.

Drain lines run under the slab too, and they can leak as well, but those behave differently. This guide is mostly about pressurized supply lines, since those are the ones that leak around the clock and drive up the bill.

The signs, roughly in the order people notice them

No single sign proves a slab leak. A few of them together, especially combined with a failed meter test, make it very likely.

A water bill that jumps for no reason

This is usually the first clue. Your household hasn’t changed, nobody’s filling a pool, and the bill is suddenly higher than the same month last year. Pull up a few months of bills and compare gallons, not dollars, since rates change. A steady climb or a sudden step up both point to water going somewhere you can’t see.

The meter moves when nothing is on

If every faucet, toilet, appliance and irrigation zone is off and the meter is still turning, water is leaving the system. We cover the full test in the next section because it’s the single most useful thing a homeowner can do before calling anyone.

A warm spot on the floor

If the leak is on a hot water line, the water running under the slab heats the concrete above it. People notice it barefoot, or they see the dog or cat suddenly favoring one patch of tile. It’s often a strip rather than a single spot, following the route of the pipe.

Running water sounds with everything off

Late at night when the house is quiet, stand in different rooms and listen. A faint hiss or a sound like a trickle inside a wall or under the floor, with no fixtures running, is worth paying attention to. Pressurized water escaping through a small opening can be surprisingly loud right above it.

Cracked tile or lifting flooring

New cracks in tile, grout that crumbles in one area, or wood and laminate that starts cupping or swelling can mean moisture is coming up from below. Tile cracks happen for plenty of other reasons, so treat this as a supporting sign, not proof.

Mildew smell or damp carpet

Carpet that feels damp along an interior wall, a musty smell in one room that won’t go away, or baseboards that are swelling or stained at the bottom. In our climate everything smells a little humid sometimes, but a smell that stays in one spot is different.

Water pooling outside near the foundation

Water that travels under a slab often comes out at the edges. A patch of soil along the house that stays wet when it hasn’t rained, or a spot where the irrigation clearly isn’t reaching, can be leak water surfacing.

Lower water pressure

A big enough leak steals pressure from the rest of the house. If showers feel weaker than they used to and it’s happening at more than one fixture, it’s worth running a meter test. If only one faucet is weak, that’s more likely an aerator or cartridge problem.

A water heater that runs constantly

When a hot line leaks, the water heater keeps refilling with cold water and keeps heating it. A tank that cycles on all the time, a gas burner you hear more often, or an electric bill that rises alongside the water bill are all signs that hot water is going somewhere. A tankless unit firing with no taps open is an even clearer signal.

How to do a water meter test

This takes about 30 minutes, most of it waiting. You’ll need to find your water meter, which for most city-supplied homes in Southwest Florida is in a box near the street or at the edge of the property. Homes on private wells won’t have a utility meter, and we’ll touch on that below.

• Turn off everything that uses water. That means every faucet, the dishwasher, the washing machine, the ice maker, and any irrigation running off potable water. Make sure no toilets are refilling.
• Open the meter box lid carefully. Watch for ants, wasps and the occasional toad. Wipe the glass face if it’s dirty.
• Find the low-flow indicator. On many meters it’s a small triangle, star or gear on the dial that spins with even a tiny flow. If you don’t see one, use the smallest sweep hand.
• Watch the indicator for a full minute. If it’s moving, water is flowing somewhere.
• Write down the full reading, then wait 15 to 30 minutes without using any water and read it again. Any change is a leak somewhere past the meter.
• If the meter moved, find your main shutoff at the house and turn it off. Check the meter again. If it stops, the leak is inside the house side of the system. If it keeps moving, the leak is likely in the line between the meter and the house.

A moving meter doesn’t automatically mean the slab. The most common culprit is a toilet flapper leaking into the bowl. Put a few drops of food coloring in each toilet tank, wait 15 minutes without flushing, and see if color shows up in the bowl. If it does, fix that first and test again.

Also check the water heater relief valve discharge pipe and any outdoor hose bibs. If all of those are dry and the meter is still moving with the main open, a hidden line is a strong possibility, and that’s when professional leak detection makes sense.

On a well system, you can’t do this test with a utility meter. Instead, watch the pressure gauge on the pressure tank with everything off. If pressure keeps dropping and the pump kicks on with no water being used, something is leaking.

Hot side or cold side, and why it matters

Once you know there’s a leak, the next question is which line. You can get a rough answer yourself. Turn off the cold water supply at the top of the water heater, leave the main on, and check the meter again. If the meter stops, the leak is likely on the hot side. If it keeps moving, it’s probably on the cold side.

Hot water leaks tend to show themselves faster because of warm floors and a hard-working water heater. They also cost more month to month since you’re paying to heat water that goes into the ground. Cold water leaks can run quietly for a long time, sometimes only showing up on the bill.

Hot lines also tend to fail more often. Heat expands and contracts the pipe every time hot water runs, and where a copper line rubs against concrete or gravel, that movement slowly wears through the wall of the pipe.

Why slabs in Southwest Florida leak

There isn’t one reason. It’s usually a mix of the pipe material, the age of the house and what’s around the pipe.

• Age and material. A large share of homes built in the region before the 2000s have copper supply lines running under the slab. Copper lasts a long time, but decades of use, water chemistry and contact with concrete and fill can thin the walls until pinholes form.
• Abrasion. Pipes laid on fill or against rebar or stone can rub with thermal movement and water hammer. Over years, that rubbing wears a spot thin.
• Installation issues. Kinks, bends, poor joints and pipes that were nicked during construction can fail early, even in newer homes.
• Shifting soil. Our sandy soils and high water table can settle and move, especially after heavy rain or storm flooding, which puts stress on rigid lines.
• Water pressure. Pressure that’s too high, or frequent pressure spikes, puts extra load on older pipe and fittings.

If one pinhole has shown up in an older copper system, more often follow, because the same conditions affect the whole run of pipe. That’s part of the decision you’ll face after the leak is found.

What happens next: detection, then repair

The work happens in two parts. First we find the leak, then we decide how to fix it. Skipping the first part is how floors get torn up in the wrong place.

Finding the leak

Leak detection usually starts with isolating lines and pressure testing to confirm which side is leaking. From there, we use listening equipment to hear the leak through the slab, and other tools as needed to narrow it down to a small area. You can read more about how that works on our leak detection page.

Fixing it

There are generally three ways to deal with a leaking line under a slab:

• Spot repair. Open the floor at the leak, cut out the bad section, repair it and close the slab back up. This makes sense for a single leak in otherwise sound pipe.
• Reroute. Abandon the leaking section under the slab and run a new line through the walls or attic to serve the same fixtures. This avoids breaking more concrete and gets that line out of the slab for good.
• Repipe. If the pipe is aging and this is one of several leaks, replacing the whole supply system is often the better long-term move.

We go through the tradeoffs in more detail on our slab leak repair page. If repiping is on the table, our whole-house repiping page explains the process, and our guide on PEX vs copper repipes in Florida covers the material choice.

Mistakes we see homeowners make

Most of these come from a reasonable instinct to save time or money. They usually end up costing more.

• Waiting for the next bill to see if it goes away. Slab leaks almost never fix themselves. A small leak today keeps soaking the fill under your house every hour.
• Breaking the floor on a guess. A warm spot or a crack isn’t always directly over the leak. Water travels. Open the floor only after the leak has been located.
• Assuming it’s the toilet and stopping there. A toilet flapper can leak at the same time as a slab line. Fix the toilet, then retest the meter.
• Ignoring a wet patch outside. Water coming up near the foundation can be from a supply line, a drain or irrigation. Find out which before it undermines a walkway or the edge of the slab.
• Covering up the damage. Replacing a few tiles or new carpet before the leak is fixed just means doing it twice.
• Throwing away evidence. If you might file an insurance claim, keep the bills, take photos and hold on to any damaged materials until the adjuster has seen them.

Homeowner insurance, in general terms

We aren’t insurance agents and every policy is different, so read yours and talk to your agent or carrier. That said, here’s how these claims often break down, because it helps to know the vocabulary before you call.

Many homeowner policies treat the pipe itself and the work to get to it as separate things. The cost of repairing or replacing the leaking pipe is often not covered, since policies commonly exclude wear and tear and deterioration. The cost to access the pipe, sometimes called tear-out, meaning breaking and replacing the floor or wall to reach it, may be covered under some policies. The resulting water damage to the home may also be covered, depending on how long the leak has been going and the policy wording.

In Florida, tear-out coverage and water damage limits have been the subject of a lot of disputes and court decisions, and many policies now cap water damage or limit coverage for leaks that happened over a long period. That’s one more reason not to sit on a suspected leak. Report it promptly, document everything, and ask your carrier exactly what’s covered before work starts if you can.

We can give you written findings from the leak detection, showing where the leak is and what we found, which is usually what an adjuster wants to see.

Slab leaks in condos

Condos add another layer. Who’s responsible for a leak under the slab depends on where the pipe is and what your condo documents say. In Florida, the declaration of condominium and the Florida Condominium Act set out what’s part of the unit and what’s common element, along with who maintains and insures what.

Lines that serve only your unit are often the owner’s responsibility, while main lines and pipes that serve multiple units are often the association’s. But the documents control, and some buildings handle it differently. On a ground floor unit, a leak under the slab may even be coming from a line that serves units above you.

If you’re in a condo and your meter test fails, let the association or property manager know early. They may need to approve access, coordinate with neighbors, or bring in their own insurance. Getting them involved before anyone breaks concrete avoids arguments later.

New construction isn’t immune

It’s easy to assume slab leaks only happen in older houses. Most do happen in older copper systems, but newer homes can leak too. A line damaged during construction, a poorly made fitting or a kink can fail in the first few years.

Many newer homes in the area are plumbed with PEX, often run overhead through the attic instead of under the slab, which reduces the risk. But some still have lines under the slab, and drains always run there. If your house is newer and the meter test fails, don’t rule out a slab leak because of the age of the home.

After a storm or flooding

Hurricanes and heavy flooding can shift soil under slabs and stress the pipes. If your home took on water or the ground around it was saturated for days, it’s a good idea to run a meter test once things have dried out, even if you don’t see a problem. Our hurricane plumbing checklist covers what else to check after a storm.

When to call us

Call if the meter test shows a leak you can’t trace to a toilet, hose bib or outside fixture. Call if you’ve got a warm floor, a constant water heater or a wet spot that keeps coming back, even if you haven’t done the test yet. And call if you’ve already had one slab leak in an older home, since it’s worth checking the rest of the system.

HomeFlow Plumbing serves homeowners across Lee, Charlotte and Collier Counties, including Cape Coral and Fort Myers. Reach us at (239) 518-4198, email help@homeflowfl.com, or send a request through our contact page.