Warm spots, a moving meter, a rising bill: how to tell if you have a slab leak

The quick way to tell

The most reliable sign of a slab leak is a water meter that keeps moving when every faucet, toilet and appliance in the house is off. Other strong clues are a water bill that climbs without explanation, a warm spot on the floor, the sound of running water when nothing is running, and damp or warped flooring with no obvious source. If you notice two or more of these, do the meter test below today and call a plumber who uses leak detection equipment rather than guesswork.

A slab leak is simply a leak in a water line that runs beneath or within a concrete foundation. A great many homes in Dallas and across North Texas sit on slabs, and the supply lines run through or under them, so a leak there stays out of sight for a long time. The good news is that it almost always announces itself if you know what to watch for.

The clues inside the house

Slab leaks show up differently depending on which line is leaking. A hot water line leak warms the concrete above it, so you may feel a warm patch on tile or wood, or notice a pet that suddenly likes one spot on the floor. A cold water line leak is quieter and usually shows up first on the bill or the meter. Either kind can push moisture up through flooring over time.

• A water bill that rises month after month with no change in how you use water
• A warm or hot spot on the floor, often in a hallway, kitchen or bathroom
• A hissing or running-water sound in a wall or floor when everything is off
• Damp carpet, cupping or buckling wood floors, or loose tiles with no visible leak
• A musty smell or mildew along baseboards
• A water heater that seems to run constantly
• Lower water pressure at several fixtures than you used to have

The meter test that settles the question

You can confirm a leak in about two hours without any tools. The U.S. Environmental Protection Agency's WaterSense program recommends a simple version of this test: take a reading from your water meter, use no water at all for two hours, then read it again. If the reading has changed, water is going somewhere.

Most meters also have a small leak indicator, often a triangle or a little wheel, that spins when even a small amount of water is flowing. With everything off, if that indicator is turning, you have a leak somewhere between the meter and your fixtures.

• Turn off every faucet, the dishwasher, the washing machine, the ice maker and the irrigation system
• Make sure no toilet is refilling
• Find the meter, usually in a box near the street, and note the reading or watch the leak indicator
• Wait two hours without using any water, then check again
• If it moved, close the main shutoff valve at the house and check once more: if the meter stops, the leak is inside the house; if it keeps moving, the leak may be in the line between the meter and the house

Rule out the ordinary leaks first

A moving meter does not automatically mean a slab leak. The most common silent leak in a house is a toilet. WaterSense suggests putting a few drops of food coloring in the tank and waiting: if color shows up in the bowl within ten minutes, the flapper is leaking. That one costs very little to fix, and I would rather you find it yourself than pay someone to find it.

Check the irrigation system next, especially if the bill jumped in summer. A broken sprinkler head or a leaking valve in the yard can look exactly like a slab leak on the meter. Walk the yard for soggy spots. Look at the water heater's relief valve discharge line for drips, and check under every sink. The EPA estimates that household leaks waste more than 9,300 gallons in the average home every year, and most of that comes from these ordinary sources, not the slab.

If all of those are dry and the meter still moves with the house shut down, the leak is hidden. That is the point to call someone with the right equipment.

Why the pipes under a slab start leaking

The water lines in a slab are surrounded by concrete or soil, and both move. North Texas clay swells when wet and shrinks when dry, and the foundation shifts slightly with it. Over years, that movement can stress pipes at joints and bends, and a pipe that rubs against concrete or gravel can wear through. Age matters too: older copper and other metal lines can corrode, and the water chemistry in a given area plays a part.

None of this means you did something wrong. It means the system is aging. What you can control is how quickly you respond once the signs appear. A leak under a slab does not stay small, and the longer it runs, the more water goes into the soil under your house.

Call right away if water is coming up through the floor, if you hear water running under the house, or if a hot spot is getting larger. Shut off the main water valve until a plumber arrives. We answer around the clock, and we do not charge more for nights, weekends or holidays.

How we find a leak without tearing up the house

Finding a slab leak is the skilled part of the job. Opening the floor to search would be expensive and destructive, so we locate the leak first. Our leak detection equipment includes infrared cameras, which pick up the temperature difference a hot water leak creates, moisture meters, which show where flooring and walls are wetter than they should be, and tracer gas, which can be introduced into a line and detected where it escapes.

Isolating the system helps too. Testing the hot and cold sides separately narrows down which line is leaking before the exact spot is pinpointed. The result is a specific spot on the floor and a clear explanation of what is happening, so you can make a decision based on evidence instead of a guess.

The three ways a slab leak gets repaired

Once the leak is located, there are generally three paths, and the right one depends on the age and condition of the rest of the plumbing. We lay out each with the reasons and a price before any work begins.

• Spot repair: open the slab at the leak, repair or replace the damaged section, test it, and patch the concrete. This fits a single failure in otherwise sound pipe.
• Reroute: abandon the leaking line under the slab and run a new line through the walls or attic to the same fixtures. This avoids breaking concrete and makes the new line accessible in the future.
• Repipe: when the pipe has reached the end of its life and leaks keep appearing, replacing the supply piping throughout the house is often the most cost-effective long-term answer.

Choosing between a patch and a bigger fix

A spot repair is the least disruptive and least expensive option today. The question is what happens next. If the camera, pressure tests and the age of the house suggest the rest of the pipe is in good shape, a spot repair is a sensible choice. If this is the second or third leak, or the pipe shows corrosion everywhere we look, a patch often just moves the next leak a few feet down the line, and you end up paying for the floor to be opened again.

That is why I want you to see the whole picture before choosing. If a reroute or repipe makes more sense, my guide on what happens during a whole-house repipe walks through the process and what to expect while the work is done.

What a long-running leak does to the rest of the house

Water under a slab does not just waste money on the bill. It saturates the soil beneath the foundation, and in clay soil, that can contribute to foundation movement. If you are also seeing stair-step cracks in brick or doors that suddenly stick, read this foundation specialist's guide on cracks in the brick and sticking doors, and make sure the plumbing is checked before any foundation repair. Fixing the foundation while a leak keeps running is money spent in the wrong order.

Moisture rising through the slab can also damage flooring and lead to mold. If the leak has already put water into the living space, the plumbing repair is only the first step; this restoration guide on the first 48 hours after finding standing water covers drying and documentation. Whether insurance covers any of the damage depends on your policy, so call your agent early and keep photos and invoices.

What happens after you call us

When you contact us, tell us what you have noticed and whether the meter test showed movement. We schedule a visit and call ahead to confirm the arrival time. The technician isolates the system, locates the leak with detection equipment, and shows you what was found. You get the options, from spot repair to reroute to repipe, each with a job price, and nothing starts until you approve it.

After the repair, we test the system and confirm the meter stops when the house is shut down. If you want an early warning next time, ask about a smart shutoff valve that closes the water supply when it senses a leak; I cover that and other habits in my yearly plumbing maintenance checklist. We serve homes across Dallas, the Park Cities and the northern suburbs, and our work is guaranteed.

Questions people ask me