Quick answer
Common slab leak signs are warm or damp spots on the floor, the sound of running water when everything is off, a water meter that keeps moving, an unexplained jump in your bill, and musty odors. Run the meter test, shut off the main if you suspect a leak, and call a plumber. Do not break into the concrete yourself.
What a slab leak is, and whether your house has a slab
A slab leak is a leak in a supply line that is buried in or under a concrete slab floor. Because the pipe is hidden, the leak can run for a long time before anything shows on the surface.
It is tempting to assume slabs are rare in Western Washington. The sources we reviewed do not support that assumption. The National Association of Home Builders, analyzing Census Bureau data, reports that about 90 percent of new single-family homes started in the Pacific division in 2024 were built on slabs. That division is a multi-state region, the figure covers new construction only, and the analysis does not break the numbers out by Washington county. Older homes vary. The practical answer is to check your own house: look at whether there is a crawlspace hatch or a basement, and ask a plumber if you are unsure where your supply lines run.
Signs of a slab leak
No single sign proves a slab leak, and plenty of them overlap with other problems. Plumbing company guides, including Benjamin Franklin Plumbing, list the following early signs. Several together are a stronger signal than any one alone.
- Warm or cool spots on the floor that do not match your heating pattern. A Bill Howe plumber notes that hot water line leaks are easier to find because they create hot spots in the floor.
- Damp flooring when the air is dry, or darkened grout and tile edges.
- The faint sound of running water, especially at night, when no fixture is on.
- A water meter that moves when every fixture is off.
- A higher water bill with no visible explanation.
- Rising humidity or a musty smell in one room, or warped wood or buckling vinyl in one area.
- Falling pressure on a gauge. The City of Bremerton lists a leak somewhere on the property as one cause of low water pressure.
How to do the meter test
The U.S. EPA describes a simple test. It does not locate the leak, but it tells you whether water is moving when it should not be.
- Turn off every water-using fixture and appliance, including the ice maker, irrigation and the dishwasher.
- Read your water meter and write down the number.
- Wait about two hours without using any water.
- Read the meter again. If it moved at all, you probably have a leak.
- Rule out toilets first. The EPA suggests adding a few drops of food coloring to the tank. If color reaches the bowl within 10 minutes without flushing, the flapper is leaking. Flush right away so the tank does not stain.
- Optional variation from Benjamin Franklin Plumbing: check the meter overnight, then close the main valve and check again to see whether the loss stops.
What to do first
If you suspect a slab leak, the goal is to limit damage and gather information.
- Shut off the water at the main valve if you see water, hear it, or the meter will not stop. Bremerton notes the shutoff is often near the water heater, or in a garage, crawlspace, closet, cabinet or outside the foundation.
- Photograph and timestamp wet spots, meter readings and anything unusual. Benjamin Franklin Plumbing recommends this to help the plumber.
- Do not cut or break the concrete yourself. The same guide advises against concrete cutting without experience and diagnostic tools.
- Call a plumber for leak detection.
- Read your homeowner's policy or call your agent. Coverage varies by insurer. A Bill Howe specialist says insurers typically pay for locating the leak and repairing resulting damage such as drywall or flooring. The Texas Department of Insurance, in general guidance, says sudden accidental water damage is typically covered while gradual leaks and seepage are not, and that insurers may deny claims if you do not protect your property.
How plumbers locate a slab leak
Benjamin Franklin Plumbing lists several detection methods that professionals use, often in combination: pressure isolation, which shuts off branch lines one at a time while watching a gauge; acoustic listening at grid points; infrared imaging for temperature differences; tracer gas; moisture meters; and a small test core when needed.
A Bill Howe specialist describes a similar sequence for cold water lines. The technician pressurizes the line using a gauge on an outdoor hose bib, checks whether the reading drops, tests fixtures one by one, and then uses electronic sound equipment to pinpoint the spot under the concrete. Which methods fit your house is a decision for the plumber after seeing the layout.
Repair options in general
Sources use different names for the same ideas, so expect your plumber to explain the terms. The broad choices are below, and the right one depends on how many leaks there are, the condition of the pipe and what the floors look like.
- Direct or spot repair: open the floor over the leak, replace the damaged section, pressure-test and patch. Benjamin Franklin calls this the least disruptive choice for one short run or a single joint. Bill Howe describes it as the most common commercial solution, with the floor opened by jackhammer.
- Reroute: abandon the leaking line under the slab and run new pipe overhead or through accessible areas such as a crawlspace or the slab perimeter. Bill Howe calls this the most common residential solution, and notes it is less invasive for flooring. Benjamin Franklin notes it can still require drywall or cabinet work.
- Repipe: replace more of the system, which Benjamin Franklin says is typical when there are multiple leaks or severe corrosion. Bill Howe describes it as a long-term option that reroutes all the lines under the slab.
- Epoxy or clamp repair: described by Benjamin Franklin as suitable only for minimal damage in an accessible spot where the rest of the pipe is sound.
- Whichever route is chosen, Benjamin Franklin recommends finishing with pressure and moisture testing.
Why not to wait
Leaks waste water even when they are out of sight. The EPA estimates that the average household loses more than 9,300 gallons a year to leaks, and that about 9 percent of homes leak 50 gallons or more per day. A slab leak can also damage flooring and encourage mold in the affected area. Texas Department of Insurance guidance is that gradual leaks are generally not covered by home policies, so a slow leak left alone can leave you carrying the cost.
When to call Pyper Plumbing
Call if the meter moves with everything off, you hear water you cannot account for, a floor spot is warm or damp, or your bill jumps without a reason. Pyper Plumbing provides leak detection and repair across Snohomish, Skagit, Whatcom and Island counties, and a plumber can walk through the repair options that fit your home.
If water is actively spreading, shut off the main valve first, then call. Tell us what you saw, what the meter did during the test and when the signs started. Pyper does not do gas line, septic, well pump, HVAC or electrical work, so if you have a heating system in or under the floor, a heating contractor is the right call for that part.
Common questions
How do I know if I have a slab leak?
Look for several signs together: warm or damp floor spots, running water sounds with everything off, a meter that moves during the two hour EPA test, and an unexplained bill increase. A plumber has to confirm the leak and its location.
Can I do the water meter test myself?
Yes. The EPA describes turning off all water use for about two hours, then rereading the meter. If the reading changed, you probably have a leak. Check toilets first, since a leaking flapper can look the same.
Will insurance cover a slab leak?
It depends on the policy. A Bill Howe specialist says insurers typically cover finding the leak and repairing resulting damage. The Texas Department of Insurance says sudden accidental water damage is generally covered and gradual leaks generally are not. Ask your agent.
Do I need to repipe the whole house for a slab leak?
Not always. Sources describe spot repair, rerouting and full repiping as separate options. Repiping is described as typical for multiple leaks or severe corrosion. A plumber can say which fits after locating the leak.
Sources
Facts in this guide come from the following references. Local rules and manufacturer instructions can differ, so follow your utility and your equipment manual.
- Fix a Leak Week (U.S. EPA WaterSense)
- Foundation Type by Region (National Association of Home Builders)
- Slab Leak Detection: Early Signs and Repair Options (Benjamin Franklin Plumbing)
- All About Slab Leaks: Your FAQs Answered (Bill Howe Plumbing)
- Water Pressure (City of Bremerton)
- Unexpected indoor waterfall? Home or renters insurance might help (Texas Department of Insurance)
This guide is general information, not a substitute for an on-site inspection. If you smell natural gas, leave the building and call 911 or your gas utility. Pyper does not perform gas line work.
