Many homes, especially in the South and West, are built on a concrete slab with water lines running underneath it. When one of those lines leaks, the water has nowhere obvious to go, so a slab leak can run for weeks before anyone notices. Catching it early limits the damage and keeps your repair options open.
Warning signs of a slab leak
- A water bill that jumps without any change in how you use water.
- Sound of running water when every faucet, toilet and appliance is off.
- Warm spots on the floor, often a sign of a leak in a hot water line. Pets sometimes find them first.
- Damp or warped flooring, loose tiles, or carpet that's wet with no spill.
- Low water pressure throughout the house.
- A water heater that runs constantly, because it keeps reheating water leaking out of the hot line.
- Cracks in walls or the slab, or mildew smells near the floor.
The water meter test
This simple test tells you whether water is leaving your plumbing when nothing should be running:
- Turn off every faucet, appliance, irrigation system and ice maker. Make sure toilets aren't refilling.
- Find your water meter, usually in a box near the street, and note the reading. Many meters also have a small triangle or dial (the leak indicator) that spins with even small flows.
- Wait at least an hour without using any water, then check again.
If the reading changed or the leak indicator moved, water is going somewhere. It might be a running toilet or an irrigation line rather than the slab, so check those next. To narrow it down, close the main shut-off valve to the house: if the meter keeps moving, the leak is likely between the meter and the house. If it stops, the leak is inside the home's plumbing, which includes lines under the slab.
Hot or cold line?
Turn off the water supply valve to your water heater (usually on the cold inlet pipe at the top) and repeat the meter test. If the leak stops, it's probably on the hot side. That's useful to tell the plumber, and hot water line leaks also explain warm spots and a constantly running water heater.
How plumbers find the leak
Professional leak detection uses acoustic listening equipment, pressure tests on individual lines and sometimes thermal imaging to pinpoint the leak, often within a foot or two, without breaking the floor. Leak detection and foundation inspection typically cost $300 to $750, and it's money well spent: guessing wrong means breaking concrete in the wrong place.
Your repair options and what they cost
| Method | How it works | Typical cost |
|---|---|---|
| Direct access | Break the slab over the leak, repair the pipe, patch the concrete | $700 – $5,000 |
| Epoxy pipe lining | Coat the inside of the existing pipe, no digging | $500 – $3,500 |
| Rerouting | Abandon the line under the slab and run new pipe through walls or the attic | $3,900 – $7,500 |
| Whole-house repipe | Replace all supply lines, usually overhead | $4,000 – $15,000+ |
Direct access usually makes sense for a single leak in otherwise sound pipe. Rerouting or repiping makes more sense when the pipes are old, corroded, or have already leaked before, because another leak under the slab is likely. Compare all three in the slab leak repair cost calculator, and see our PEX vs. copper repiping guide if you're weighing a repipe.
Insurance: what's usually covered
Homeowners policies vary, but a common pattern is:
- Often covered: sudden water damage to floors, walls and belongings, and sometimes the cost to break and restore the slab to reach the leak.
- Often not covered: replacing the pipe itself when it failed from age or corrosion, and damage from a leak that went on for a long time.
- More likely covered: leaks caused by a covered event, such as an earthquake, frozen pipes or a falling tree.
Call your insurer before repairs start, photograph everything, and keep all invoices. Act quickly: a leak you knew about but didn't fix is harder to claim.
What to do right now
- If water is visibly damaging the home, close the main shut-off valve. See what to do before the plumber arrives.
- Move furniture and rugs off wet flooring and start drying the area.
- Schedule professional leak detection rather than a general plumber's guess.
- Get at least two quotes for the repair, especially if rerouting or repiping is recommended.
Frequently asked questions
How do I know if I have a slab leak?
Common signs are an unexplained jump in your water bill, the sound of running water when everything is off, warm or damp spots on the floor, and low water pressure. A water meter test with all fixtures off is a simple first check.
How much does it cost to fix a slab leak?
Typical costs are $700 to $5,000 for direct access, $500 to $3,500 for epoxy lining, and $3,900 to $7,500 to reroute the line. Leak detection usually adds $300 to $750.
Is a slab leak an emergency?
A small slab leak isn't usually an immediate danger, but it wastes water and can damage flooring and foundations over time. If water is surfacing or flooring is soaked, shut off the main valve and call a plumber right away.
Will homeowners insurance pay for a slab leak?
Often the resulting water damage is covered, while the pipe repair itself may not be if it failed from age. Coverage depends on your policy and the cause, so call your insurer before work starts.
Sources: HomeGuide, slab leak repair costs.