The short answer: The most common signs of a slab leak are a water bill that jumps for no clear reason, a water meter that keeps moving when nothing in the house is running, a warm spot on the floor, the sound of running water when everything is off, and damp flooring or baseboards that keep coming back. You can safely check your meter and look for these clues yourself. Confirming a leak under concrete, and finding exactly where it is, takes a licensed plumber with leak-detection equipment.
Here’s how it usually starts. You walk across the kitchen barefoot and one patch of tile feels oddly warm. Or the water bill arrives at nearly double last month’s, and nobody changed anything.
The first instinct is often to start pulling up flooring. Please hold off. Water under concrete can travel, so the wet spot you see may not be where the pipe broke.
Below: what each sign can (and can’t) tell you, a simple meter test you can do this afternoon, what to leave alone, and how the repair choice affects your floors and walls afterward.
What is a slab leak?
If your home sits on a concrete slab, some of its water lines may run under or through the concrete. A slab leak is a leak in one of those lines, and because the concrete hides it, water can escape for weeks before you notice.
This Old House lists common causes including corrosion (especially in copper and galvanized steel pipe), abrasion, high water pressure, poor installation, and ground movement from soil, earthquakes, or tree roots.
What are the signs of a slab leak?
Any one of these signs can have an ordinary explanation, so the table shows both.
| Sign | What it could point to | What else could cause it |
|---|---|---|
| Water bill higher than usual, with no change in use | Water escaping somewhere on your property | A running toilet, an irrigation leak, a seasonal or rate change |
| Water meter moving when nothing is on | A leak somewhere past the meter | Toilets, irrigation, an outdoor line, an appliance |
| A warm spot on the floor | A leak in a hot water line below | Ducts or radiant heat, sun through a window, a nearby appliance |
| Sound of running water when everything is off | Water moving through a pipe | A toilet tank refilling, irrigation |
| Damp carpet, swollen baseboards, or flooring that lifts or cups | Water reaching the floor from below | A leak inside a wall, an appliance line, moisture coming up through the slab |
| Water heater running more than usual | Hot water escaping | An aging water heater, more household use |
One sign on its own is rarely proof. Two or three together, especially a moving meter plus a warm or damp spot, is a strong reason to call a plumber.
If the water is showing up overhead instead of underfoot, our guide on what to check when you find a water stain on the ceiling walks through that situation.
How can I check for a leak with my water meter?
This is the most useful free check you can do. The U.S. EPA’s WaterSense program puts it simply: “Check your water meter before and after a two-hour period when no water is being used. If the meter changes at all, you probably have a leak.” Long Beach Utilities gives similar steps and adds that if the meter moves right away with everything off, you likely have a fast-moving leak.
- Find your meter. It’s usually in a box near the street or sidewalk. Lift the lid carefully and look before you reach in.
- Turn off everything that uses water. Faucets, showers, dishwasher, washing machine, irrigation timer, ice maker, and any pool or fountain auto-fill.
- Take a photo of the reading. Many meters also have a small low-flow indicator that turns with even a trickle.
- Wait two hours without using any water.
- Read the meter again. Any change suggests a leak somewhere past the meter.
The meter test tells you water is going somewhere. It doesn’t tell you where. A few safe ways to narrow it down:
- Toilets. Listen for hissing or a tank that refills on its own. Long Beach Utilities warns that a leaky toilet can waste 180 gallons of water per hour.
- Irrigation. Walk the yard for soggy spots or water running to the sidewalk when sprinklers are off.
- The house shutoff. If your home has a main shutoff valve where the line enters the house, close it and watch the meter again. If the meter still moves, the leak may be in the line between the meter and the house (or an outdoor line that branches off before it) rather than under the slab. If it stops, the leak is more likely somewhere in the home’s own plumbing.
One caution: only turn a valve that moves easily by hand. Older valves can break or start leaking when forced. If it’s stiff, stop and let a plumber handle it.
Why does my floor feel warm in one spot?
A leak in a hot water line can warm the concrete above it, so a warm patch on tile or wood is one of the classic slab leak clues. But not every warm spot is a leak. Some homes have heating ducts or radiant heat in or under the floor, and afternoon sun can warm a floor for hours.
Check the spot at different times of day, including early morning before anyone has used hot water. Notice whether your water heater runs when no one is using hot water.
What should I avoid doing myself?
- Don’t break up concrete or pull up flooring to search. You may open the wrong area. In older homes, some flooring and adhesives can contain asbestos, and the EPA advises against sanding or scraping materials that may contain it.
- Don’t ignore water near electrical. Keep people away from wet outlets, cords, or appliances. Only switch off a breaker if you can reach the panel while standing somewhere dry.
- Don’t let wet materials sit. The EPA says “it is important to dry water-damaged areas and items within 24-48 hours to prevent mold growth.” Move rugs and furniture off damp spots and run fans while you wait for help.
Who do I call first?
Usually in this order:
- A licensed plumber or leak-detection specialist to confirm and pinpoint the leak, using tools such as pressure testing, listening equipment, or a video camera.
- Your insurance agent, early, if there’s water damage.
- A drying or water damage company if flooring, drywall, or cabinets got wet.
- A general contractor to put things back: flooring, drywall, paint, baseboards, and sometimes cabinets.
What are the repair options, and how do they affect my house?
Your plumber will recommend an approach based on where the leak is, the pipes’ condition, and the house layout. Each option leaves different work behind.
| Repair option | What happens | What it affects afterward |
|---|---|---|
| Direct repair through the slab | The concrete is opened over the leak, the damaged section is replaced, and the slab is patched | Flooring in that area comes up and has to be replaced |
| Reroute | The leaking line is abandoned and new pipe runs through walls, ceilings, or the attic | Drywall openings to patch and paint; floors usually stay put |
| Pipe lining | The pipe is cleaned and sealed with a lining from the inside | Fewer openings, but it depends on pipe condition |
| Repipe | Much or all of the water piping is replaced, usually through walls and ceilings | Several wall openings and a larger patch-and-paint job |
What does it cost? This Old House (page updated May 2026) cites Angi contractor estimates showing most homeowners pay about $630 to $4,400 for slab leak repair, with an average around $2,300 and some jobs as high as $6,750. Those are national figures, not Southern California quotes, and they don’t include leak detection, new flooring, drywall repair, or water damage cleanup. Ask for a written, itemized quote.
Permits. Pipe replacement often needs a plumbing permit. The Los Angeles Department of Building and Safety, for example, says plumbing permits are required to install or modify potable water piping. Other cities set their own rules, so ask your plumber whether a permit will be pulled.
If the slab got wet and you’re replacing the floor, don’t rush new flooring down. Our guide to the best flooring over a concrete slab explains why testing the slab’s moisture first matters.
Does homeowners insurance cover a slab leak?
It depends on your policy. Policygenius, an insurance comparison site, explains that policies generally don’t pay to fix the broken pipe itself, but may cover tearing out the slab to reach it and resulting water damage from a covered event. Slow leaks and wear and tear are commonly excluded. Call your agent before repairs start, take photos, and keep the plumber’s written findings.
Also call your water utility. Long Beach Utilities, for example, says the property owner is responsible for pipes past the meter, but it offers a partial bill adjustment for qualifying hidden or underground leaks that are repaired promptly, with proof. Other utilities set their own rules.
When can I handle it myself, and when should I call a pro?
You can usually handle: the two-hour meter test, checking toilets and irrigation, tracking your bills, photographing warm or damp spots, moving rugs and furniture, running fans, and calling your insurance agent.
Call a pro for: confirming and locating the leak, any concrete cutting or pipe repair, a shutoff valve that won’t turn, water near electrical, mold larger than a small patch (the EPA uses about 10 square feet as a rough line), and replacing flooring, drywall, and finishes afterward.
Frequently asked questions
How do I know if I have a slab leak? Look for a combination of clues: a meter that moves when no water is in use, a higher bill with no change in habits, a warm or damp spot on the floor, or the sound of running water. Only a plumber with leak-detection equipment can confirm it.
Why is one spot on my floor warm? A leaking hot water line can warm the concrete above it. Ducts, radiant heat, sunlight, or a nearby appliance can also warm a floor, so check at different times of day before assuming the worst.
Is a slab leak an emergency? It can become one. If water is coming up through the floor, near electrical, or the meter is spinning quickly, close the main shutoff if it turns easily and call a plumber right away.
Does homeowners insurance cover slab leak repair? Often not the pipe itself, but some policies cover access and resulting water damage from a sudden covered event. Coverage varies, so call your agent before repairs start.
Dealing with the damage a slab leak left behind?
Once the plumber fixes the leak, the house still has to be put back together: floors, walls, and sometimes cabinets. If your pipes have failed more than once and you were already planning a kitchen or bath remodel, it can make sense to plan the pipe work and the remodel together, so walls only get opened once.
De Sisto Construction, Inc. is a California licensed general contractor (CSLB #803545) serving greater Los Angeles and Orange County since 2001. We put together step-by-step outlines and line-item project costing, so you can see what the repair and restoration involve before work begins. Take a look at our residential remodeling services, including kitchens, bathrooms, and full home renovations.
Give us a call at 562-425-1050 or email us at info@desistogc.com (dcidirect.net)