Slab leak signs are easy to miss because the leak is under your floor, inside the concrete. A line under the slab can run for months before a warm spot or a water bill jump gives it away. In Dallas-Fort Worth, where almost every home sits on a slab over clay soil, it is one of the most common plumbing repairs we do. Here is what to watch for, how a plumber confirms it, and what decides the repair.
In short
- Watch for a water bill up 20 percent or more with no change in use, warm spots on the floor, a water heater that never shuts off, and a meter that moves with every fixture closed.
- DFW clay soil can move several inches between wet and dry seasons, which stresses the copper lines under homes built before 1980.
- A plumber confirms a slab leak with a hydrostatic test, electronic listening equipment, and a sewer camera before anyone cuts concrete.
- Repairs are a spot fix, a reroute, or a tunnel under the house. The pipe, the location, and the floor above decide which.
Slab leak signs DFW homeowners notice first
Two or three of these together mean it is time to call. The EPA WaterSense program estimates household leaks waste nearly 10,000 gallons of water per year in the average home, and about 10 percent of homes have leaks wasting 90 gallons a day or more. A slab leak is often why a home lands in that 10 percent.
Changes you can see or feel
- Warm or hot spots on the floor. A hot water line is the most common culprit. If a patch of tile is warm in a room with no floor heat, mark it.
- Damp carpet, cupped wood, or lifting tile, often along a wall or near a bathroom.
- Cracks wider than 1/8 inch. Hairline cracks are normal. New cracks past 1/8 inch, or doors that suddenly stick, point to wet soil moving the foundation.
- Mildew smell with no source, or water pooling along the foundation outside.
Changes you can measure
These slab leak signs do not depend on luck. Check them before you call so you can give the plumber real numbers.
- Water bill. Compare this month with the same month last year. An unexplained rise of 20 percent or more justifies a leak test.
- Meter test. Shut every fixture off, including the ice maker and irrigation, and watch the meter for 15 minutes. If the low-flow dial moves, water is leaving the system.
- Water heater run time. A tank that cycles constantly, or a tankless unit that fires with no tap open, means hot water is going somewhere. Our water heater team sees this weekly.
- Water pressure. A gauge on a hose bib should read 40 to 80 psi. Below 40 psi with normal city supply suggests a leak big enough to drop pressure.
For walls and attics too, see our post on spotting hidden plumbing problems.
Why DFW homes get slab leaks
Expansive clay soil
Most of Dallas, Fort Worth, Plano, Frisco, and Arlington sits on Blackland Prairie clay. It swells when wet and shrinks when dry, and between a wet spring and a hot August it can move several inches. Texas A&M’s Transportation Institute has documented this shrink-swell behavior for decades. The slab rides up and down with the soil, and the pipes under it bend, rub on concrete, and crack at a joint or wear a pinhole.
Slab-on-grade construction and older copper
Nearly every DFW home built since the 1960s is slab-on-grade, with supply lines under the concrete. Homes built before 1980 usually have soft copper under the slab, and copper wears where it touches rebar, corrodes from soil chemistry, and pinholes from high-mineral water (our post on hard water in Texas explains why). Newer homes with PEX fare better, though drain lines under any slab can still separate when the soil moves.
How a plumber confirms slab leak signs
A proper slab leak inspection finds what, where, and how bad before anyone cuts a floor. We use three tools.
| Test | What it checks | What you learn |
|---|---|---|
| Hydrostatic test | Drain and sewer lines under the slab | Whether the drain system holds water. A drop in level over 15 to 20 minutes confirms a leak. |
| Electronic leak detection | Pressurized supply lines | The leak’s location, usually within a foot or two, by listening and by isolating hot and cold lines. |
| Sewer camera | Inside the drain pipe | The exact failure: a separated joint, a crack, a root, or a collapsed section. |
The hydrostatic inspection comes first when symptoms point to a drain: a sewage smell, slow drains in more than one room, no hot spot. If it fails, we run a camera through the cleanout (our guide to finding your sewer line cleanout shows where builders put them). Supply leaks go straight to electronic detection. Both tests belong in a pre-purchase plumbing inspection, and many DFW buyers now require a passed hydrostatic test before closing.
Repair options and what drives the cost
Spot repair
The plumber opens the slab above the leak, replaces that section of pipe, and pours new concrete. Fastest when the leak sits under a cheap floor finish. A poor choice for old copper, because a second leak a few feet away is likely.
Reroute
The failed line is abandoned and a new one runs through the attic or walls to the same fixtures. No floor is opened and the whole run is replaced, which matters in a pre-1980 home. Our usual choice for hot water lines.
Tunneling
A crew digs under the foundation from outside, repairs the pipe, and backfills. It protects finished floors and is usually the only route for a sewer line repair under a slab, since drain lines cannot go overhead. It takes longer and costs more.
What affects the price
Supply or drain line, pipe depth, distance from an outside wall, the flooring above (carpet is cheap to restore, tile and hardwood are not), and pipe age. We quote every slab leak repair after the inspection, never over the phone, because those details change the answer. Our plumbing services page lists what the visit includes. Home insurance often covers the damage but not the pipe repair, so check your policy early.
Slab leak signs FAQ
How fast should I act on slab leak signs?
Within days, not weeks. A supply leak runs 24 hours a day and the wet soil keeps moving the foundation. Shut off the main at night until the plumber arrives.
Can I tell if the leak is on the hot or cold line?
Usually. Close the cold inlet valve on the water heater and recheck the meter. If it stops, the leak is on the hot side. If it keeps moving, it is on the cold side or a drain.
Does a hydrostatic test damage the pipes?
No. It fills the drain lines to slab level, the same pressure they see every day. It cannot find supply leaks, so electronic detection is a separate step.
Will a slab leak show on a foundation inspection?
Not reliably. A foundation company measures elevation and cracks; a plumber tests the pipes. If a report shows movement near a bathroom or kitchen, get a plumbing test before paying for piers.
Think you have a slab leak?
The Right Choice Heating and Air tests and repairs slab leaks across Dallas, Fort Worth, Arlington, Plano, Frisco, Carrollton, Farmers Branch, Irving, and nearby. Call (214) 251-4015 or schedule a slab leak inspection online. We find the leak first and quote the repair after the inspection.