Slab leak signs: how to tell if a pipe under your floor is leaking

What is a slab leak?

Homes built on a concrete slab, with no crawl space or basement, often have their water supply lines running beneath or inside that slab. A slab leak is a break in one of those buried lines. Because the pipe is under concrete and flooring, water can escape for weeks before anything shows on the surface. The leak can be on the hot side, the cold side, or a drain line, and each one gives slightly different clues.

Newer construction is not immune. The median home in Murrieta was built in 2000, in Temecula in 1998 and in Wildomar in 1994, according to census-based figures, while Oceanside's median home dates to 1984 with about 38 percent of homes built before 1980. Older piping has had more time to wear, but a slab leak can show up in a house of any age.

Which signs matter most?

Some signs point strongly to a hidden leak; others have many possible causes. This table ranks them roughly by how much they tell you.

HomeAdvisor lists the same core warning signs: warm or damp floors, standing water, sudden pressure changes, unusually high bills, and hearing water when nothing is running.

How do you run the meter test?

The EPA's WaterSense program describes a simple test, and it is the best first step before paying anyone:

1. Make sure nothing uses water: faucets, toilets, the dishwasher, the washing machine, the ice maker, the irrigation controller and any softener regeneration.
2. Find the meter. Most are in a box near the street at the front of the lot.
3. Write down the reading or take a photo.
4. Wait two hours without using any water, then read it again. If the number changed, you probably have a leak.

If the meter moved, close the house main shutoff and repeat the test. If it still moves with the house valve closed, the leak is likely in the line between the meter and the house rather than under the slab, which is a yard water line repair. If it stops when the house valve is closed, the leak is inside the house: a running toilet, a dripping fixture, or a pipe in the slab or walls.

The EPA also suggests looking at winter bills. A family of four using more than 12,000 gallons in a month like January or February likely has a serious leak. EPA estimates that household leaks waste more than 9,300 gallons per home each year, and that about 9 percent of homes have leaks wasting 50 gallons or more per day.

Is the leak on the hot side or the cold side?

A warm floor and a water heater that seems to run all the time point to the hot line. To test it, close the cold inlet valve on top of the water heater and watch the meter. If the meter stops, the leak is on the hot side. If it keeps going, the leak is on the cold side or somewhere else. Knowing which line is involved narrows the search and can affect the repair choice.

What happens once you suspect a slab leak?

The next step is professional leak detection. A technician uses acoustic listening equipment, pressure testing of individual lines, and sometimes thermal imaging to find the leak through the floor. HomeAdvisor reports that leak detection averages about $280, with most homeowners paying $150 to $400.

Once the leak is located, there are three general ways to fix it:

• Direct repair: cut through the floor and slab at the leak, repair the pipe and patch the concrete. Best when the leak is in an accessible spot and the rest of the pipe is sound.
• Reroute: abandon the leaking section and run a new line through walls or the attic. Avoids breaking concrete, and often the better choice when the line is old.
• Repipe: replace most or all of the supply piping when leaks keep recurring. The City of Oceanside handles residential re-pipe permits through its eTRAKiT system.

National figures from HomeAdvisor's 2025 cost guide give a sense of scale:

Those figures do not include flooring replacement or drying, which can add a meaningful amount when the leak sits under finished tile or hardwood. For how local labor rates compare, see the Oceanside plumber cost guide.

Who pays, and what about permits?

A pipe under your slab is private plumbing. The City of Oceanside tells homeowners that water and sewer lines on their property are their responsibility to repair, and Fallbrook Public Utility District says leaks on the customer side of the meter are the customer's to fix. Keep the plumber's invoice and the leak detection report either way.

Homeowners insurance is written around sudden and accidental water discharge, according to the National Association of Insurance Commissioners. Ask your insurer how it treats a leak that has been running under the floor, and whether it pays to open and restore the slab and flooring even if the pipe repair itself is not covered.

Permit rules vary by city. In Murrieta, replacing a defective concealed pipe counts as new work that needs a permit and inspection, while simple leak repairs that do not replace or rearrange pipes are exempt. Ask anyone offering slab leak repair in Temecula or leak detection in Murrieta whether the planned work needs a permit and who pulls it.

What should you avoid?

• Ignoring a moving meter. A slow leak under a slab keeps wetting the soil and flooring, and the bill keeps climbing.
• Breaking concrete on a guess. Locate the leak first. Opening the wrong spot adds cost without fixing anything.
• Patching the same line repeatedly. A second or third leak on the same run usually means a reroute or whole-house repiping costs less over time.
• Waiting on a fast leak. If water is coming up through the floor, close the main and follow the steps in our burst pipe guide.

If the meter test points to a leak under the floor, an independent plumber who handles slab leak repair in Oceanside can confirm it, locate it and explain the options. Homeowners in Encinitas can find Encinitas slab leak specialists, and those in Wildomar and nearby Riverside County towns can use the same process.