Think You Have a Slab Leak? Start at the Water Meter

A slab leak means a water line under the concrete floor has sprung a leak, and most houses north of Orlando sit on just that kind of slab. You can't see under the concrete, so guessing from a damp spot or a warm tile isn't enough. The good news: the EPA's WaterSense program and Seminole County both describe free meter checks that tell you whether water is leaving the pipes when nothing is running.

What is a slab leak, in plain terms?

It is a leak in a pressurized water line that runs below or through the foundation slab. In many block houses, supply lines were laid before the concrete was poured, so a leak there can run for a while without showing on the surface. Drain lines can fail under a slab too, but those don't spin the water meter, so the checks below are about supply lines.

We could not find a neutral, primary source that lists reliable warning signs, so we won't give you a checklist of symptoms. A damp floor, a hot spot, a hissing sound or a mildew smell can come from many things. Treat them as reasons to run the meter test, not as a diagnosis.

How do I check the meter for a hidden leak?

The meter test is the one check with solid backing. EPA's version is simple: jot down the reading, run nothing for a couple of hours, and check whether it moved. Any change at all likely means a leak.

Seminole County's version is faster. With every tap, appliance and sprinkler off, head to the meter box out by the street or sidewalk and raise the meter's cap. Underneath is a flow indicator: a tiny dial, triangle or wheel. If it is spinning while everything is off, water is going somewhere.

Is the leak inside the house or out in the yard?

Close the house's main shutoff valve and watch the flow indicator again. Seminole County says that if it still moves with the main valve closed, the leak is outdoors, somewhere between the meter and that shutoff. If it stops, the leak is on the house side, which could mean a fixture or a line under the slab.

Before blaming the slab, rule out the easy things. The county's page lists items that refill on their own: a pool, a fountain, a softener, an ice maker and the water heater. Toilets are the big one; a toilet can silently leak 150 gallons a day. Do EPA's dye test, and shut off toilets one at a time at their supply valves to see if the indicator stops. Our story on a high water bill covers these checks in more detail.

When do I stop and call a licensed plumber?

When the meter says there is a leak and the easy checks don't find it. Seminole County's own advice is plain: if none of the tests finds your leak, it is time to call the plumber. Locating a leak under concrete takes equipment and training, and only a licensed plumber should cut into a slab or reroute a line.

While you wait, you can close the main shutoff between uses to limit the water lost. That is all the homeowner work we suggest. Check the plumber's license first; our hiring a plumber story shows how to read a Florida license number.

What repair choices might a plumber offer?

We found no neutral source comparing repair methods, so we can't tell you which one fits your house. A plumber may talk about fixing the one spot under the floor, or about running a new line through the walls or attic instead. Ask what each choice involves, whether it needs a permit, and what happens to the old line. Seminole County's building division keeps an illustrative list of work that needs a permit and says to call if you're unsure.

If your house is old enough to have polybutylene pipe, the conversation may turn to replacing more than one leak. That is a bigger decision, and it is worth getting it in writing.

Does insurance cover a slab leak?

That depends on your policy, so ask your agent. What we can say: since February 2022, Citizens has asked for a 4-point report, plumbing included, once a house passes 20 years of age. Keep the plumber's written findings and any meter readings with your records.

Can a leak under the slab cause a hole in the yard?

It can contribute. The Florida Geological Survey lists collapsed or broken sewer and drain pipes and broken septic tanks among causes of ground depressions that are not true sinkholes. If a hole opens near the house, keep people and pets away, don't pour water into it, and read our sinkholes and pipes story.

Readers often ask

Can I find a slab leak myself with a moisture meter or by feel?

You can notice things, but you can't confirm a slab leak that way. The meter test tells you water is leaving the pipes; pinpointing where under the concrete is a job for a licensed plumber with the right equipment.

My meter box has two meters. Which one do I watch?

Two meters can be the house and the irrigation, or yours and a neighbor's. Seminole County says its billing office can confirm which one is yours from the number on the meter cap.

Should I shut the water off at the main until the plumber comes?

Closing the main shutoff between uses limits lost water and is safe homeowner work. Open it again when you need water, and leave cutting, digging and line work to the plumber.

Is a warm spot on the tile floor proof of a hot-water slab leak?

No. We found no neutral source that treats it as proof, and floors warm up for other reasons. Run the meter checks and let a licensed plumber test the hot and cold lines.

Does a slab leak always mean the whole house needs new pipes?

Not necessarily. We found no neutral source comparing repair choices, so ask the plumber to explain each option for your house in writing, along with any permit it needs.

Where this came from

1. EPA WaterSense — Fix a Leak Week — two-hour meter test, toilet dye test
2. Seminole County Water Conservation — Leaks (archived 2025) — flow indicator check, main shutoff test, toilet leak figure, auto-refill items, when to call a plumber
3. Seminole County Building Division (archived 2026) — permit list is illustrative; call if unsure
4. Citizens Property Insurance — 2022 rates and rules bulletin (archived) — 4-point inspection for homes over 20 years old
5. Florida Geological Survey — Sinkhole FAQ — broken pipes among causes of ground depressions
6. Florida DBPR — Construction Industry Licensing Board (archived 2026) — plumbing license types