Signs of a slab leak in a Florida home, and what happens next

Almost every house in Lee and Collier County sits on a concrete slab poured over sand. The water lines that feed the kitchen and bathrooms often run under that slab, and when one of them leaks there is no basement to flood and no ceiling stain to point at it. The water goes into the sand, the slab wicks it up, and the first sign is usually something that does not look like plumbing at all.

What a slab leak looks like from inside the house

• A warm spot on the floor. If the leak is on the hot side, the water heats the slab above it. On tile you feel it barefoot, and pets tend to find it first. This is one of the most reliable tells.
• The sound of running water with everything off. Stand quietly with all faucets closed and the washer and dishwasher idle. A faint hiss or rush in the floor or the bottom of a wall is water moving under pressure.
• The meter keeps moving. With the house valve open and every fixture shut off, the small dial or the flow indicator on the meter should sit still. If it creeps, water is leaving the system somewhere.
• Damp baseboards and low drywall. Water moving through the slab shows up where the floor meets the wall: swollen baseboard, a stained or bubbling paint line, tile grout that stays dark.
• A mildew smell with no source. Water under a slab has nowhere to go but up into the flooring and the bottom of the walls.
• Cracks, heaving, or a soft spot. A long-running leak can wash sand out from under the slab or swell it, and tiles crack or lift along a line.
• A drop in pressure at one or several fixtures with no other explanation.
• A water heater that never rests. A hot-side leak pulls hot water out around the clock, so the heater cycles constantly and the electric bill climbs alongside the water bill.

One sign alone can be something else. A warm floor can be a hot line running normally close to the surface, and a high bill is more often a toilet. Two or three together, and a slab leak moves to the top of the list.

The fifteen-minute meter test

1. Turn off every fixture, the icemaker line if you can reach it, and the irrigation.
2. Find the meter at the street and note the reading, or watch the low-flow indicator, the small triangle or star on a dial meter.
3. Wait fifteen minutes without using water.
4. If the reading changed or the indicator turned, close the main valve at the house and check again. If the meter stops, the leak is inside the house or under it. If it keeps moving, the leak is in the yard line between the meter and the house.

Rule out toilets before you go further. Put a few drops of food coloring in each tank and wait ten minutes; color in the bowl means a flapper is leaking, and that is a much smaller problem.

Why Southwest Florida homes get slab leaks

Copper was the standard for supply lines in homes built here from the 1960s into the 1980s, and much of it went in as soft copper tubing laid directly in the sand under the slab before the pour. Soft copper sits in contact with wet, sometimes salty fill and with the concrete itself. Over decades it pits from the outside in and from the inside out, since our treated water is chlorinated and on the hard side. Anywhere the tube rubs against the slab as it expands and contracts with hot water, the wall thins. Add a kink from installation, and forty years is about all it has.

How the leak gets found

Guessing where to cut a slab is usually wrong, so the job starts with detection. A plumber isolates the hot and cold sides and pressure tests each one to confirm which line is leaking. Then an electronic listening device, essentially a very sensitive ground microphone, is moved across the floor to find where the hiss is loudest. On a hot-side leak, a thermal imaging camera shows the warm plume through the tile. On a suspected drain leak, a camera goes down the line and a dye or smoke test confirms it.

The result is a mark on the floor, often within a foot or two of the leak, before a single tile comes up. This is not a homeowner job. The equipment is specialized, and the reading takes practice to interpret through tile, thinset, and concrete. Your part ends at the meter test and the toilet test.

Three ways to fix it

• Spot repair through the slab. Open the floor at the mark, dig to the pipe, replace the failed section, and pour back the concrete. Least disruption to the rest of the house, but the flooring at that spot is sacrificed, and on old copper the next leak is often a few feet away.
• Reroute overhead. Abandon the leaking line under the slab and run a new PEX line through the attic and down the wall to the fixture. No jackhammer, no digging, and the new line is where it can be reached. On a one-story slab home this is often the sensible choice.
• Whole-house repipe. When the slab leak is the second or third leak, or the home still has all its original copper, replacing every supply line through the attic ends the pattern instead of chasing it.

Which one makes sense depends on the age of the pipe, how many leaks the house has had, and what the floors mean to you. A good detection visit ends with that conversation, not just a mark on the tile.

Insurance, briefly

Many Florida policies treat the water damage and the access as covered and the pipe repair itself as excluded, and some carriers have added exclusions for older plumbing or specific materials. Before any work starts, photograph the damage, the meter, and the detection mark, and read your policy or call your agent. A licensed plumber’s written detection report is what the adjuster wants to see.

If you have a warm spot, a moving meter, or a smell you cannot trace, send us a note with what you have found and when it started. We will tell you whether it sounds like a slab leak and what the next step looks like.