The carpet near the hallway feels damp. The water bill is up, and late at night, with every tap off, you think you hear water running somewhere. Most people check the toilets and faucets first, and that’s the right instinct. When those check out fine, the problem may be under your feet.
So how do you know if you have a slab leak in your home? You rule things out in order. A slab leak is a water line that’s failed under the concrete your house sits on, and it gives itself away through your meter, your floors, and your ears. This guide walks you through the checks in the order we’d run them, what each one tells you, and when it’s time to call a licensed plumber.
Step 1: Rule out the toilets
A running toilet is the quietest water thief in a house, and it’s far more common than a slab leak. Drop food coloring in the tank, don’t flush, and look in the bowl in fifteen minutes. Color in the bowl means the flapper is passing water. That’s a cheap fix you can do yourself, and if it explains the high bill, you’re done.
Step 2: Let your water meter tell you
Your water meter will tell you about a leak before your eyes will. Here’s how to read it.
- Shut off every faucet, the ice maker, the irrigation, and any appliance that uses water.
- Find your meter, usually in a box near the street, and look for the small triangle on its face.
- Watch the triangle for a few minutes. If it’s moving, water is going somewhere.
- Close the main shutoff where the line enters the house and look again. If the meter still moves, the leak is in the line between the meter and the house. If it stops, the leak is inside the house, and that includes under the slab.
A moving meter proves water is leaving the system. It doesn’t prove the leak is under the slab, and it doesn’t tell you where. What it gives you is solid evidence instead of a hunch, and that’s worth having when you call a plumber.
Step 3: Walk the floors and listen
Feel for warm spots
Walk barefoot across tile, hardwood, or vinyl, ideally in the morning before the house warms up. A spot that feels warmer than the floor around it points to a hot water line leaking under the slab. On carpet, feel for damp or spongy areas instead. Mark anything suspicious with painter’s tape so you can show the plumber.
Look for damp flooring and new cracks
Damp carpet with no spill to explain it, wood or vinyl that starts to cup or lift, and new cracks in tile or grout near the floor all mean water has been running long enough to reach the surface. A musty smell in a room that never flooded belongs on the list too.
Listen with everything off
With the house quiet and nothing running, listen near the bathrooms, the kitchen, and the water heater. A steady hiss or trickle from the floor, one that doesn’t stop after a toilet refills, is a strong sign of a pressurized leak below you.
Step 4: Figure out if it’s a water line or a drain line
They behave differently. A water line is pressurized, so it shows up as a water bill that jumped or a warm spot on the floor, and the meter keeps creeping with everything off. A drain line is quieter: repeat backups, or damp carpet in one spot, with a meter that doesn’t move. If your signs point to the drain side, our sewer and slab services page covers what happens next.
What happens if you wait
A water line under the slab is under pressure all day and all night, so a leak never takes a break. It soaks the concrete, the flooring above it, and the soil below it. Our Tulsa clay already moves with the wet and dry cycles, and a leak washing out the soil under a slab gives it one more reason to shift. Moisture trapped under flooring can also feed mold long before you see it.
The repair gets bigger with time too. The longer a leak runs, the more flooring, drywall, and cleanup get added to the job, and those costs come on top of the plumbing.
How we confirm a slab leak
Your checks tell you something is wrong. Ours tell you exactly where. We isolate the hot and cold sides and pressure test each one, which takes the search from somewhere under the house to a single line. Then we pinpoint the spot with acoustic gear that hears water under concrete. On a drain line, a camera with a sonde on the head marks the spot and depth in paint on your floor.
We don’t cut until we know where the leak is, so the opening stays small. We also photograph what we find on every leak call, which helps if you end up filing an insurance claim. Read more about our slab leak detection.
If it is a slab leak, what are your options?
Once the leak is found, there are three ways to fix it, and we do all three in house.
- Open the slab and replace the section: we cut the concrete over the leak from inside the house, replace the failed pipe, and put the concrete back. Best for a single failure on a line that’s otherwise sound.
- Reroute through the attic: we take the failed run out of service and run a new line overhead, usually PEX. Often the better call when the leak sits under finished flooring or the same run has leaked before.
- Repipe the house: when leaks show up in different parts of the house inside the same year, patching one more won’t solve it. A whole-home repipe typically takes 1 to 3 days, and we turn the water back on before we leave every evening.
For a whole-home repipe, our own Tulsa job history puts the average at $5,000 to $7,000, with large, difficult homes at $15,000 or more. For a single slab leak, we find it first, then walk you through the options and the cost before any work starts. Our leak repair and repiping page has more on how we decide.
What to do right now
If you find water where it shouldn’t be, shut the water off at the main. It’s usually where the line enters the house, in a garage, utility closet, or outside wall. Get the floor dry and put a fan on it, because water sitting turns a pipe bill into a drywall bill. Write down what you’ve noticed (warm spots, the meter, any sounds, the bills) and then call a licensed plumber.
The bottom line
If you’ve been asking, “How do I know if I have a slab leak in my home?”, start with the toilets, then the meter, then the floors. If the toilets are fine and the meter moves with everything off, it’s time for a plumber with the right equipment. A slab leak is a serious problem, but it’s a solvable one, and waiting only makes it bigger.
Tulsa Plumbing & Remodeling is licensed and insured (Oklahoma plumbing license #180753), with same-day service and no pricing games. Call us at (918) 800-4426.
