What is a slab leak?
A slab leak is a leak in a water line that runs through or beneath the concrete foundation of a home. Many single-story houses in the Reno area are built slab-on-grade, which means hot and cold supply lines are laid in the gravel and soil before the concrete is poured. When one of those lines develops a pinhole or a cracked joint, the water has nowhere to go but into the soil, the slab and eventually your flooring.
Slab leak detection is the work of finding that leak from above the floor, without tearing up rooms to look for it. The goal is a single marked spot, usually accurate to a small area, so the repair can be planned around it. That might mean a small opening in the slab, or bypassing the line entirely. It is one of several services in leak detection in Reno, and it is the one that saves the most flooring when done early.
How does slab leak detection work?
Providers rarely rely on one tool. They stack tests, and each one shrinks the search area.
- Confirm the leak. With every fixture off, the water meter is checked for movement. If it moves, water is escaping somewhere on the pressurized side.
- Isolate the line. The hot and cold sides are shut off separately, and each is pressure-tested with a gauge. A line that loses pressure is the leaking one. This step also tells the technician whether the problem is under the slab or elsewhere.
- Trace the pipe route. Electronic line locators follow the pipe under the floor so the technician knows where to listen and scan.
- Listen through the concrete. Ground microphones amplify the hiss of water escaping under pressure. The sound is loudest right above the leak.
- Scan for heat. For hot water lines, thermal imaging shows a warm bloom on the floor surface that lines up with the leak.
- Confirm with tracer gas if needed. On quiet or very slow leaks, a safe gas mix can be pushed through a drained line and detected where it escapes through the slab.
If the warm spot is near your water heater or kitchen, mention it on the call. It helps the provider decide whether to start with the hot side.
What are the warning signs of a slab leak?
Slab leaks give off clues long before water shows. Watch for these eight signs:
- A warm or hot spot on the floor that stays warm at night or in shade.
- A water meter that keeps moving when nothing in the house is running.
- The sound of running water under the floor when the home is quiet.
- A water bill that jumps with no change in how you use water.
- Cracked or loose tile, or grout that suddenly breaks apart in one area.
- Damp, swollen or warped flooring, such as laminate that lifts at the seams.
- A water heater that runs constantly, or hot water that runs out sooner than it used to.
- Mildew smell or damp carpet pad with no leak from a fixture above.
One sign alone can have another cause. Two or more together point strongly to a line under the slab.
What causes slab leaks in Reno homes?
Most slab leaks come from slow wear rather than one big event. Copper lines under a slab can rub against gravel or the concrete itself as the pipe expands and contracts with hot water. Over years, that friction thins the wall of the pipe until it opens.
Water chemistry plays a part too. Reno-area water is known for being hard, and mineral-heavy water combined with high velocity at bends and fittings can wear pipes from the inside. Poor installation, kinked lines, or pipes laid without sleeves where they pass through concrete add stress. Ground movement and settlement can shift the slab slightly and pull on joints.
Hot water lines fail more often than cold ones because heat speeds up wear and causes more expansion. That is why a warm floor is such a common first clue.
What can you safely check before calling?
You can confirm a likely slab leak in about an hour without tools:
- Turn off every faucet, appliance, ice maker and irrigation zone.
- Find the water meter and note the reading or watch the small leak indicator.
- Wait 30 to 60 minutes with no water use, then check again.
- Walk the floors barefoot and feel for warm areas, especially near the kitchen, bathrooms and water heater.
- Shut the valve on the water heater's cold inlet. If the meter stops moving, the leak is likely on the hot side.
Do not drill, chip or cut the slab to look for the leak. Without an exact location, you risk hitting the line, rebar or a post-tension cable.
What happens during a professional slab leak visit?
A typical visit follows a clear order. The technician asks about your symptoms, then checks the meter to confirm water is being lost. Next, they isolate and pressure-test the lines to find which side is leaking. Once they know the line, they trace its route under the floor and use acoustic gear and thermal imaging along that path.
When the loudest point and the heat signature line up, the leak is marked on the floor, often with tape or a marker. A good provider then explains what they found and lays out repair options. Those usually include a spot repair through a small opening in the slab, a reroute that runs a new line through the walls or attic, or a repipe if several lines are failing. The leak repair page explains how those choices compare. Ask for photos and written notes of the findings for your records and any insurance claim.
What affects the cost of slab leak detection?
| Factor | How it affects the job |
|---|---|
| Hot vs. cold line | Hot lines are often faster to find with thermal imaging. Cold lines can take more acoustic work. |
| Flooring type | Thick tile, wood or carpet over pad can muffle sound and heat. |
| Leak size | Very slow leaks are quieter and may need tracer gas. |
| Home layout | Long pipe runs and multiple branches add testing time. |
| Visit timing | Evening, weekend or emergency calls usually cost more. |
Prices are set by each independent provider, so ask what the detection fee covers before the visit.
When is a slab leak an emergency?
Treat it as urgent if water is pooling on the floor, if a hot water leak is making a room noticeably hot, or if the meter is spinning fast. Shut the main water valve, turn off power to an electric water heater or set a gas heater to pilot, and call right away. Water under a slab can wash out soil and damage flooring quickly. A slow leak with no visible water is still worth booking soon, but it rarely needs a midnight visit.
Related services and nearby areas
Slab leaks often show up alongside other problems. If the meter moves but the slab tests dry, the issue may be in the buried service line between the meter and the house, which is what water line leak detection covers. If you see stains on walls near a bathroom, hidden pipe leak detection traces leaks inside framing. Newer slab-on-grade neighborhoods such as Damonte Ranch, South Meadows and Spanish Springs see a lot of slab calls. For the full picture of how detection works across the city, see our Reno leak detection guide.
