What Are the Signs of a Slab Leak Under My House?
Last updated October 28, 2026
The short answer
Why Slab Leaks Are Tricky
A slab leak happens when a pipe under your concrete foundation starts to drip or burst. Because the water is hidden below the slab, you might not see a puddle or a stain right away. The leak can go on for weeks before you notice anything unusual.
Your home's foundation sits directly on the ground, so water from a leak can soak into the soil and spread out. The concrete hides the evidence, but the water still finds a way to show itself through floors, walls, and your utility bills. Pay attention to small changes, they often point to a bigger problem.
Signs You Should Not Ignore
One of the clearest signs is a warm spot on your floor, especially if you have heated floors or hot water pipes under the slab. Another is a hissing or trickling sound that continues even after you turn off all faucets and appliances. That noise often means water is moving somewhere it should not.
Check your water meter with everything off. If the dial still moves, you have a hidden leak. Also look for cracks in your foundation walls, tile, or drywall. Water pressure from a leak can shift the ground and cause these materials to break.
- Warm or damp patches on your floor
- Sound of running water when nothing is on
- Unexplained increase in your water bill
- New cracks in foundation, tile, or drywall
- Musty smell in a room that stays dry otherwise
What Causes a Slab Leak
Slab leaks often come from corroded copper pipes, shifting soil that bends a pipe, or poor installation work. In areas with wet winters and dry summers, the ground can expand and contract, putting stress on your plumbing. Over time, that stress can cause a weak point to fail.
The age of your home matters too. Older pipes are more likely to develop pinhole leaks or joint failures. If your home is in Redmond, keep a record of your plumbing's age and any past repairs. That history can help you decide whether to monitor or replace aging pipes.
How to Check for a Leak Yourself
Start by shutting off all water-using appliances and fixtures in your home. Then find your water meter and watch the low-flow indicator. If it spins or moves, you have a leak somewhere. You can also listen near your floors with a stethoscope or a glass to catch the sound of dripping.
Feel your floors with your bare hands or feet, especially in hallways, bathrooms, and near the water heater. A warm or cold spot that stands out from the rest of the floor is a strong clue. If you find one, mark the spot and contact a local water damage pro for a closer look.
Why You Should Act Quickly
A slab leak does not fix itself. The longer water flows under your foundation, the more it can erode the soil, weaken the slab, and cause mold to grow in your subfloor. That can lead to expensive repairs and health concerns for your family.
If you suspect a leak, shut off your main water valve right away to limit the damage. Then call a professional who can use special tools to pinpoint the exact spot. Acting fast can save you from tearing up your whole floor and dealing with a bigger mess.
Talk to someone now
Water keeps spreading into floors and walls, so it is worth acting early. Calls are answered 24/7.
Call Now (425) 407-5186Frequently asked questions
Can a slab leak cause mold under my house?
Yes. Moisture from a slab leak can seep into your subfloor and create a damp environment where mold grows. You might notice a musty smell or see dark spots on your drywall. If you feel unwell from the smell, see a doctor.
How do pros find a slab leak without tearing up my floor?
Professionals use electronic listening devices, thermal cameras, and pressure testing to locate the leak. These tools let them pinpoint the exact spot, so they can make a small access hole instead of breaking up the whole slab.
Will my insurance cover a slab leak?
Policies vary, and your insurer decides what is covered. Some home insurance covers sudden, accidental water damage from a burst pipe, but not gradual wear and tear. Check your policy and talk to your insurance company to understand your situation.