How do I know if I have a slab leak?
A warm or damp patch on the floor, running water you can hear but not see, a musty smell, or cracking in flooring above the leak.
This one can get worse fast. Call before it spreads.
Key takeaways
- This is an emergency. Shut things down and call a plumber now rather than waiting.
- Most likely cause: Corroded copper supply line under the slab.
- Do this first: Shut off every fixture and watch the meter for movement.
- Call right away if water is coming up through the slab or into finished flooring.
- The repair starts with: Confirm the loss with a meter and pressure isolation test.
What it is
Slab leak A slab leak is a leak in a water or drain line that runs beneath the concrete foundation of the home, often revealed by a warm spot on the floor, the sound of running water with no fixture on, or a rising water bill.
This needs immediate action, so shut off the main water supply if you suspect a slab leak, since it can undermine the foundation and cause serious damage the longer it runs undetected.
The short answer
A slab leak is a water line failure under the concrete foundation. The classic signs are a warm spot on the floor, the sound of running water with everything shut off, a jump in the water bill, unexplained damp carpet, and a drop in water pressure. Run the meter test to confirm water is moving with every fixture closed. Slab leaks do not stop on their own, and the longer one runs the more damage it does to the foundation and flooring.
Call now, do not wait on a form
We answer 24 hours a day, every day, across the Denver metro.
What it usually means
These are the causes we find most often, ranked from most likely to least.
- 1
Corroded copper supply line under the slab
Most likely
Age and soil chemistry pit the pipe until it fails.
- 2
Abrasion where pipe moves against concrete or rebar
Common
Expansion and contraction wear a hole over the years.
- 3
Soil movement stressing the line
Common
Expansive Front Range soils shift and pull joints apart.
- 4
High water pressure
Less common
Excess pressure accelerates every weakness in the buried run.
- 5
Poor original installation or a damaged line from construction
Occasional
Shows up years later once the damaged section finally fails.
What to do right now
- 1Shut off every fixture and watch the meter for movement.
- 2Feel the floor for warm spots, which usually indicate a hot side leak.
- 3Listen for running water at night when the house is quiet.
- 4Shut off the main if water is visibly coming up through the floor.
When it is an emergency
- Water is coming up through the slab or into finished flooring.
- Foundation cracks appear or widen alongside the leak.
- You cannot stop the meter from running even with the main partly closed.
What the fix involves
Location comes first. Electronic and acoustic detection pinpoints the leak so the repair opens as little concrete as possible. From there the options are a spot repair through the slab, rerouting the line above the slab, or repiping the affected run, and the right choice depends on the age and condition of the rest of the piping.
- 1Confirm the loss with a meter and pressure isolation test.
- 2Pinpoint the leak with electronic leak detection.
- 3Choose between spot repair, reroute, or repipe.
- 4Complete the repair, pressure test, and restore the opened area.
What drives the cost
Every job is quoted before work begins. These are the factors that move the number on this kind of repair.
- Spot repair through concrete versus reroute versus repipe
- Depth of the slab and flooring type above it
- Leak detection time on a hard to locate leak
- Concrete and flooring restoration
Related problems homeowners ask about
Why did my water bill suddenly go up?
A bill well above the seasonal norm with no change in usage, sometimes with a warm floor spot, a damp yard, or the sound of running water.
Read this nextWhy is water pressure low in my whole house?
Weak flow at every tap, showers that lose force when another fixture runs, and appliances that take much longer to fill.
Read this nextWhat causes a ceiling stain under an upstairs bathroom?
A brown ring, a soft or sagging spot, bubbling paint, or active dripping on the ceiling directly under a bathroom.
Read this next
Read more on this
This page is for triage and dispatch. These guides go deeper on how the work is done and what shapes the price.
Licenses, credentials, and company proof
- Colorado Master PlumberLicense MP-18927
- Colorado State Plumbing ContractorLicense 2110
- Family Owned & OperatedServing Denver since 2006, 20 years
- Better Business BureauAccredited Business, A+ rating
- Angie's List Super Service Award2012 through 2017
- Serving Denver since 2006Residential and commercial properties across the metro
Tell us what is happening
Send the details and we will get back to you with next steps and a free quote. If it is urgent, calling is faster.
Get A Free Quote
We reply fast. Same day when possible.
Before you book: pricing, timing, and guarantees
Straight answers on what leak under slab work costs, how fast we can get out, and what stands behind the repair.
More plumbing help from Afford-A-Rooter
- Ceiling Stain From Bathroom AboveBrown ring on the ceiling below a bathroom in Denver? Learn the ranked causes, why a bulging ceiling is urgent, and how the leak gets located.View page
- Sump Pump Not Turning OnSump pump not running while the pit fills in Denver? Learn the ranked causes, the bucket test, and what to do before the basement floods.View page
- Water Heater Making Popping NoisePopping or rumbling from your Denver water heater usually means sediment. Learn what it does to the tank, when flushing helps, and when to replace.View page
- Tankless Water Heater InstallationInstalling a tankless water heater in Denver? Get sizing for real winter inlet temps, gas and venting done right, and a free quote. Call (720) 296-7972.View page
- Water Heater ReplacementReplace your Denver water heater before it leaks. Gas, electric, and tankless options, permitted installs, old unit hauled away. Call (720) 296-7972.View page
- 40 vs 50 Gallon Water HeaterShould you buy a 40 or 50 gallon water heater? Learn how first hour rating, bathroom count, and gas vs electric recovery decide the right size.View page
Stop guessing and get it diagnosed
Family owned, licensed Colorado master plumbers serving the Denver metro since 2006.