Short answer
A warm spot on the floor, water running with every faucet off and a jump in the water bill are the classic signs of a slab leak. Turn everything off and check the water meter: if the leak indicator spins, there is a leak. Close the cold water valve on top of the water heater: if the meter stops, it is a hot line. Then call a plumber who does leak detection.
How to tell if you have a slab leak
1A warm spot on the floor and water running
The floor feels warm in one spot (the cat loves it) and you hear water running with everything off. A hot water pipe under the slab is the usual suspect.
Read all the steps
- A warm spot on the floor and water running. The floor feels warm in one spot (the cat loves it) and you hear water running with everything off. A hot water pipe under the slab is the usual suspect.
- Turn everything off and check the meter. With no water in use, look at the meter. If the leak indicator keeps spinning, water is escaping somewhere.
- Close the valve on top of the water heater. Turn the cold water valve that feeds the heater clockwise. If the meter stops and the warm spot cools down, the leak is on a hot water line.
- Do not break up the floor to look. Pipes under a slab are hard to locate. Breaking concrete on a guess makes a bigger mess and can miss the leak completely.
- A leak detection pro pinpoints it. They listen to the floor with sensitive equipment and use pressure tests or thermal cameras, then mark the exact spot to repair or reroute.
- Call a plumber who does leak detection Especially if: the meter moves with every faucet and appliance off.
Plumbers near you
Share your location and we will show the nearest ones with their phone number.
Or pick your city:
Other signs of a slab leak
- A water bill higher than usual with no change in habits.
- Damp carpet, warped wood floors or cracks in the tile.
- Low water pressure, or a water heater that runs all the time.
- A mildew smell or puddles at the base of the walls.
What the fix looks like
A plumber can open the floor at the exact spot and repair the pipe. Or they can reroute the line through the walls or the attic and leave the old one in place. Rerouting is common when the pipes are old or have leaked before. Ask which one they recommend and why.
Until it is fixed
If the leak is on the hot side, keep the valve on the water heater closed and set the heater to "vacation" or turn off its breaker. If water shows up on the floor, close the main valve whenever you are not using water.
When to call a plumber
- The meter moves with every faucet and appliance off.
- You find a warm spot on the floor or hear water running nonstop.
- Floors are damp, warped or cracking for no clear reason.
- The water heater runs all the time even when nobody uses hot water.
Frequently asked questions
What does a slab leak sound like?
Like a faucet running somewhere far away, or a faint hiss, even when all the water is off. It is easiest to hear at night when the house is quiet.
Why is one spot on my floor warm?
A hot water pipe leaking under the slab warms the concrete above it. If the spot is warm and the meter shows a leak, call a plumber who does leak detection.
How do plumbers find a slab leak?
With acoustic listening gear, pressure tests on each line and sometimes thermal cameras. They mark the spot before any concrete is opened.
Is a slab leak an emergency?
It is urgent, but rarely a same-hour emergency unless water is coming up through the floor. Close the water heater valve or the main to slow it and book a plumber soon: water under the slab can damage floors and the foundation.
Does homeowners insurance cover a slab leak?
Many policies pay to open the floor and repair the water damage, but not the pipe itself. Check your policy and call your insurer before work starts.
Can I fix a slab leak myself?
No. Finding it takes special equipment, and the repair means cutting concrete or rerouting pipes. Your part is spotting the signs and doing the meter check.