Slab leak signs
Leaks under a slab are hidden by concrete and flooring, so they show up indirectly. Several of these together are a strong signal.
- A warm or hot spot on the floor, usually over a hot-water line.
- The sound of running water with every fixture turned off.
- A water meter that moves when nothing is running.
- A water heater that seems to run all the time.
- Damp or warped flooring, or a musty smell with no visible source.
- A sudden rise in the water bill.
Confirming and locating the leak
The plumber first proves the leak with a meter test, the same one EPA recommends to homeowners: read the meter, use no water for a period, read it again. Then comes isolation: closing the water heater's cold inlet shows whether the leak is on the hot side, and pressure tests on individual lines narrow it further. Acoustic listening and thermal imaging then pinpoint the spot. Fixr's guide puts detection at $100 to $400. More on the tools is on our leak detection page.
Repair methods and their costs
| Method | National range |
|---|---|
| Sealing a minor leak | $100–$200 |
| Patching the pipe | $250–$800 |
| Repairing a broken pipe section | $200–$2,000 |
| Lining the pipe from inside | $500–$2,000 |
| Breaking the slab to reach the leak | $500–$3,000 |
| Tunneling under the slab from outside | $900–$2,000 |
| Rerouting the line overhead | $4,000–$15,000 |
Source: Fixr national slab leak guide, updated May 1, 2025. National average $2,500; typical range $1,000–$4,000. Flooring replacement is separate.
Spot repair or reroute: how to decide
A spot repair fixes the leak you have. A reroute replaces the line that produced it. The choice turns on what the rest of the buried pipe is likely to do.
- How many leaks has this line had? A first leak in otherwise sound pipe is a good candidate for a spot repair. A second or third on the same line points to corrosion along its length.
- What is the pipe? Soft copper under slabs can pit from the inside and fail in more than one place; our page on pinhole leaks in copper pipe explains why.
- What is on top of the leak? Breaking through tile or hardwood in a kitchen adds flooring cost that can close the gap to a reroute.
- Hot line or cold? Hot lines fail more often and waste energy while they leak. Some owners reroute the hot side and leave a sound cold side alone.
What a reroute involves
Rerouting abandons the buried pipe where it is and runs new pipe, usually PEX, from the point where the water enters the house to each fixture through walls, the attic or crawl-accessible spaces. There is no concrete work, but there are drywall openings to patch. When most of the house's lines are rerouted at once, the job becomes a partial repipe, and the numbers on our repipe cost page become the better comparison.
Questions to ask before approving the work
- How was the leak located, and how precise is the location?
- Is the quote for the leak alone, or for the whole line?
- Who repairs the concrete, and who handles the flooring?
- Is a permit needed for the reroute in your jurisdiction?
- What warranty covers the repaired section, and does it cover the rest of the line?
Slab leak questions after the diagnosis
How long does the repair take?
A spot repair through the floor is often done in a day, plus time for the concrete patch to cure before flooring goes back. A reroute of one line usually takes one to three days, depending on how many walls and ceilings the new pipe crosses.
Will a reroute show inside the house?
The new pipe runs through walls, the attic or ceilings, so there will be small openings to patch and paint. A good crew plans the route to use closets and cabinet backs where it can.
Can a slab leak damage the foundation?
A leak that runs for a long time can wash out or swell the soil under a slab. Cracks in floors or walls near the leak area are a reason to have the slab looked at once the plumbing is fixed.
Is it safe to wait a few weeks?
It is rarely a good idea. The water bill keeps climbing, a hot-side leak keeps the heater running, and water under the slab keeps spreading. Shut off the affected line if the plumber can isolate it, and schedule the repair.
Sources
- Slab Leak Repair Cost, Fixr, updated May 1, 2025.
- Fix a Leak Week, U.S. Environmental Protection Agency, updated March 13, 2026.
Reviewed September 27, 2026. Found an error? Write to admin@plumbingrepairquotes.com.