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A slab leak is a leak in a water line that runs under or through your home’s concrete foundation. Because the pipe is buried, water can escape for weeks before anything shows on the surface. In South Florida, where most houses are built slab-on-grade, it’s one of the most common hidden leaks.
These are the signs to watch for, roughly in the order people notice them.
The 7 most common signs
1. Your water bill goes up for no reason
A leak under the slab runs 24 hours a day. Even a small one can add a noticeable amount to your bill. If your usage hasn’t changed, treat a jump as a warning. Our high water bill guide walks through the meter test.
2. A warm spot on the floor
If a hot-water line is leaking, the water heats the concrete above it. You may feel a warm patch on tile, especially barefoot, or notice a pet always lying in the same spot.
3. The sound of running water
With every faucet and appliance off, listen near the floor at night. A hiss or trickle you can’t trace is a common clue.
4. Damp carpet, swelling wood or loose tile
Water pushes up through the slab and soaks flooring from below. Wood floors may cup or swell, and tile can crack or sound hollow when tapped.
5. The water meter moves when nothing is on
This is the most reliable at-home test. Turn off all water, then watch the leak indicator on your meter for two minutes. If it moves, water is going somewhere.
6. The water heater runs constantly
A leaking hot-water line means the heater keeps refilling and reheating. You might hear it cycle more often or see higher energy costs.
7. Mold, mildew or a musty smell
Constant moisture under flooring encourages mold, especially in Florida humidity. A new musty smell near baseboards is worth checking.
Why slab leaks happen
- Older copper or galvanized pipes thinning over time
- Pipes rubbing against concrete or gravel as the house settles
- Poor original installation or kinked lines
- High water pressure stressing joints
What to do if you suspect one
- 1
Do the meter test
Confirm water is being lost before anything else.
- 2
Note the details
Where is the floor warm or wet? Is it hot water or cold? When did you first notice?
- 3
Shut off hot water if needed
If you suspect a hot-water leak, closing the cold supply valve on top of the water heater stops more hot water from flowing to the leak.
- 4
Call for slab leak detection
A specialist can pinpoint the leak with pressure tests, acoustic equipment and thermal imaging, so only a small section of floor is opened.
Don’t start breaking tile
Guessing where the leak is can mean several holes instead of one. Pinpointing it first keeps the repair smaller. See slab leak detection in Coral Gables.
Common questions
Can a slab leak fix itself?
No. Pressurized water lines keep leaking, and the damage usually grows over time.
Is a slab leak an emergency?
A large or hot-water slab leak should be handled quickly. Even a small one is worth locating soon, before it damages flooring or causes mold.
