A slab leak occurs when a water pipe that is connected to your house under the concrete foundation begins leaking. It will not be visible in the field. Rather, you’ll discover things such as increased water bills, warm areas on the floor, or the sound of running water when no taps are running. If these warning signs are caught early, your foundation and wallet could be spared from disaster.
What Is A Slab Leak, Exactly?
A slab leak occurs when the water supply or drain pipe that runs under a concrete slab foundation has a break, crack or pinhole. The hot and cold water lines for most homes that are built on a slab traverse or pass under the concrete. If one of those pipes are corroded, moves or is damaged during construction, the water leaks away into the soil and slab rather than into the fixtures.
If left untreated, a foundation leak is not only expensive to the homeowner, it is also a waste of water. It erodes the soil beneath your house and can lead to costly structural repairs in the future, as well as cracking and settling.
9 Warning Signs Of A Slab Leak
1. Unexplained spike in your water bill
One of the easiest suspects to eliminate is a hidden leak if you aren’t using any more water than you used to but your bill has increased by 20% or more.
2. The sound of running water with everything off
Shut down all faucets, appliances and irrigation systems. When it’s still making water noises in the walls or floor, it is a red flag.
3. Warm spots on the floor
Warm or hot spots in tile, hardwood or carpet floors are often the first sign of a hot water line leak, and will be most obvious when you step onto a bare floor in the morning.
4. Cracks in walls, flooring, or the foundation itself
Pooling water under the slab will soften the soil surrounding your home. If the cracks in the drywall, baseboards or foundation are new, you should have your home inspected.
5. Damp carpet, buckling floors, or mold odors
Moisture rising through the slab can result in carpet moisture problems with no apparent water damage, the hardwood or laminate can warp, and there may be a musty odor in a room even if one does not see any water damage.
6. Low water pressure
If water is leaking out of the pipe below ground, there will be less pressure at the fixtures. A sudden drop in pressure should be investigated, either at a single tap or in the whole house.
7. The sound of your water meter still spinning
Turn off all the water at the house, and read your meter. If the dial continues to rotate, then water is moving somewhere it shouldn’t.
8. Mold or mildew where it shouldn’t be
If mold growth is present on the baseboard or closet or along a corner of a room, but not near a plumbing fixture, it may be a sign of a slab leak under the home.
9. Pooling water around the foundation exterior
If you notice wet spots, unusually green grass or puddling water around the base of your house, particularly in dry weather, it could indicate leaking water around the foundation and into the yard.
Quick takeaway: One symptom doesn’t necessarily indicate a problem. Together, and particularly when coupled with a warm floor or new break in the crack, it’s time to call for leak detection, as two or three may indicate a leak.
Why Slab Leaks Happen
- Pipe corrosion: Copper pipes, common in older homes, corrode over 15 to 25 years, especially in areas with acidic or mineral-heavy soil.
- Ground shifting: Freeze-thaw cycles and soil movement put stress on rigid pipes running through the slab.
- Abrasion: Pipes rubbing against concrete, gravel, or rebar during minor ground shifts wear thin over time.
- High water pressure: Consistently high pressure stresses joints and weak points in the line.
- Poor original installation: Pipes installed too close to the slab surface or without proper sleeving fail faster.
How Professionals Find A Slab Leak
It’s expensive and wasteful to guess where the leak is and to begin jackhammering blindly. Licensed plumbers use:
- Acoustic listening devices that pick up the sound of water escaping under pressure.
- Electronic water leak detector and moisture leak detector tools that trace temperature and moisture differences across the floor.
- Water sensing equipment paired with pressure testing to confirm which line, hot or cold, is affected.
- Camera inspection through cleanouts to rule out sewer or drain line issues before assuming it’s a supply line.
The combination is able to locate a leak to within inches, minimizing the work required for repair crews to open the part of the slab where the leak is located.
Slab Leak Repair Cost: What To Expect
| Repair type | Typical cost range (CAD) |
| Leak detection only | $150 – $500 |
| Spot repair (accessible pipe) | $600 – $2,500 |
| Tunneling under the slab | $2,000 – $5,500 |
| Pipe rerouting above the slab | $2,500 – $6,000 |
| Full repipe | $5,000 – $12,000+ |
The true slab leak repair cost will vary based on the location of the leak, the amount of concrete that must be removed and the necessity of rerouting a pipe or the entire system. Properly diagnosing a product, not just an educated guess, ensures that minimal time is spent on opening products and thus costs are kept down.
What To Do If You Suspect A Slab Leak
- Shut off your main water valve if the leak seems active and significant.
- Note where you’re seeing warmth, dampness, or sound, this helps the plumber narrow the search.
- Avoid DIY excavation. Digging into a slab without pinpointing the leak first usually means unnecessary damage.
- Call a licensed residential plumber or commercial plumber for electronic detection rather than waiting for the problem to worsen.
- Ask about warranty coverage on any repair or repiping work before signing off.
Bos Plumbing And Drains: Local Slab Leak Experts
For more than 20 years, BOS Plumbing and Drains has been servicing the communities of Mississauga, Oakville, Brampton, Hamilton, Milton, North York, Niagara, Cambridge, Toronto and Etobicoke with leak detection near me services. Slab leaks aren’t on a business schedule so their crew provides a 24-hour plumber service to homeowners who can’t afford to wait overnight on a suspected leak.
What sets their approach apart:
- Electronic leak detection first. Acoustic and moisture sensing tools locate the exact leak point before anyone touches the slab, avoiding guesswork and unnecessary demolition.
- Upfront, transparent pricing. No hidden fees, and a free quote before work begins.
- 25-year transferable warranty on sewer and water line replacements, so a slab repair holds up long after the crew leaves.
- Licensed and insured technicians who handle both residential plumber and commercial plumber jobs, from a single pinhole leak to a full repipe.
- Fast, local response. As a Canadian-owned plumbing company, they know how freeze-thaw cycles and older GTA housing stock contribute to slab leaks in this region specifically.
When you’re seeing warm floors, a rising water bill or new cracks in your home that weren’t present last month, it’s a lot less expensive to take preemptive measures against a slab leak than to wait for it to be a foundation issue. BOS Plumbing and Drains provides free quotes and on-the-spot service, and is able to reach out to you before your small leak turns into a huge repair.