Slab Leak Detection FAQs

A slab leak is a leak in a water supply line or drain line that runs inside or underneath your home's concrete foundation. Because the pipe is buried, the leak is usually hidden until the water bill rises, a floor gets warm or damp, or the meter keeps moving with everything turned off.

Start with the meter test: turn off every faucet and appliance, note the meter reading, wait one to two hours without using water, then read it again. If it moved, water is escaping somewhere. Other common signs are a jump in your water bill, a warm spot on the floor, the sound of running water and a water heater that runs nonstop.

A warm spot on tile, wood or carpet that stays warm, especially overnight, is a classic sign of a leaking hot-water line under the slab. Hot water escaping into the soil warms the concrete above it. Thermal imaging can confirm it and trace the line.

The most common causes are expansive clay that swells and shrinks with the seasons, aging cast-iron drains in homes built before about 1980, polybutylene supply pipe from about 1978 to 1995, copper wearing against concrete or gravel, stress from foundation repair, and hard freezes. Water chemistry can add to the wear.

Yes. In newer homes, leaks usually start at a fitting, at a pipe nicked during construction, or where settling soil pulls on a line. If your home is still under a builder warranty, get the leak documented and tell the builder.

It can be either, or both. A leak can soften the soil and let part of the slab settle, and clay movement can crack a pipe. If you see new cracks or sticking doors and your water bill is also up, test the plumbing before paying for foundation work.

The plumber confirms the leak with a meter and pressure test, isolates which line is leaking, then pinpoints the spot through the concrete with acoustic listening, thermal imaging, line tracing or tracer gas. The exact spot is marked on the floor, so nobody has to break concrete to search.

Common tools are pressure gauges, acoustic ground microphones and listening discs, thermal (infrared) cameras, electronic line locators, tracer gas detectors, moisture meters and, for drains, a hydrostatic test ball and a sewer camera. Most jobs use at least two methods so the results confirm each other.

Water forced out of a pressurized pipe makes a hiss that travels through the concrete. A ground microphone amplifies and filters that sound while the plumber moves across the floor in a grid. The point where the sound is strongest marks the leak.

The line is drained and filled with a safe mix of about 5% hydrogen and 95% nitrogen. The gas escapes at the leak and works its way up through the slab, where a sensitive detector picks it up. It's useful for very quiet leaks and plastic pipe.

A hydrostatic test checks the drain and sewer lines under the slab. A test ball seals the main drain, the system is filled with water to slab level, and the level is watched. If it drops, a drain is leaking; an isolation test and camera then narrow down the section.

The meter only measures water coming into the house. A broken drain leaks water that has already been used, so it never shows on the meter. That's why drain lines are checked with a hydrostatic test instead.

Yes. Closing the cold-water inlet at the water heater shuts off the hot side. If the meter stops, the leak is on a hot-water line; if it keeps moving, it's on the cold side. Each line is then tested on its own.

No. Detection is non-invasive: it uses gauges, sound, heat and gas readings taken from inside the house and at the fixtures. The only mark left is the location of the leak on your floor, usually with tape or a removable marker.

Most slab leak detection visits cost $150–$600. The price depends on the size of the home, how many lines need testing, whether drains need a hydrostatic test, and how hard the leak is to hear. You get the price before the visit.

Most leaks are located in two to four hours. Larger homes, more than one leak, or drain testing can take longer. You get the results and the exact location before the plumber leaves.

Usually yes, because detection is a diagnostic service and the testing is done either way. If no slab leak is found, you still learn where the water isn't going, which rules out expensive guesses. Ask about the fee before the visit.

Water coming up through the floor, a sewer smell or a fast-spinning meter needs help the same day; shut off the main water valve first. A slower leak should still be checked within days, because water under a slab can wash out soil, move the foundation and grow mold.

Often in part. The Texas Department of Insurance has long said the standard HO-B policy covers damage to the dwelling, including the foundation, from an accidental discharge of water from a plumbing system. Many policies exclude wear and tear, the pipe itself and mold. Check your policy and call your insurer early.

Many Texas cities and MUDs credit part of the water lost to a hidden leak, such as a leak under the slab, once it's repaired. Most want a paid invoice and a request within a set number of days, and allow one credit a year. Call your utility for its rules.

The leak's location marked on the floor, which line is leaking (hot, cold or drain), the test readings and photos, and a written summary you can give your insurer, your water utility or the plumber of your choice.

If water is coming up through the floor, shut off the main water valve. Otherwise, do the meter test, note when you first noticed the problem, and clear access to the water heater, the main shut-off, the meter and any warm or damp spots.

Usually the property owner, because the plumbing under the slab is part of the building. Tenants should report high bills, warm floors or the sound of running water to the landlord or property manager right away; the lease sets out who arranges the work.

No. We focus only on slab leak detection. You get the exact location and a written report, and you're free to choose any licensed plumber for the repair.