At the mere mention of slab leaks the blood in my veins turns to ice and I break into a cold sweat. I hate them and I have been plagued by them!


A slab leak is the term used by the insurance and plumbing industry to describe a leak in one of the water lines that run under the concrete floor of your home. When these leaks are above the floor, they are known as pinhole leaks.


There are various theories and explanations as to what causes a slab leak: age of the piping; movement of the foundations; vibration and shifting soils leading to wear and tear; freezing of pipes; corrosion due to chemical and heat influences; high water pressure placing stress on the lines and causing leaks at the connectors; improper construction. Regardless of the reason for their existence, slab leaks are a menace and are difficult to detect, reach and repair without disruption.


These leaks are very sneaky and can easily go undetected for quite some time. The following signs may indicate that you have a leak:

  • Water where it shouldn’t be. This may seem stupidly obvious, but with slab leaks, water is not always evident. Of the three slab leaks I have experienced, only once was water actually coming through the floor.

  • A spike in your water bills should alert you that water is escaping somewhere. Slab leaks however can be slow and insidious and so you may not notice a huge difference immediately.

  • The sound of running water even when all faucets are turned off.  I could hear water running behind one of our toilets and for some time thought the toilet itself was the problem.

  • Damp drywall or baseboards that smell musty.

  • Mildew where it shouldn’t be.

  • Low water pressure in your showerheads and faucets.

  • Cracks in the walls and floor.

  • Warm spots on the floor. I noticed that one of our cats was regularly stretched out in the hallway next to one of our bathrooms. I didn’t think anything of it until I was walking barefoot on the travertine and noticed how cozy and warm it was.  Given that I don’t have underfloor heating, this is not normal!

An undetected slab leak can cause extensive damage and corrosion to your foundations, so when you do find you have one, take a deep breath and deal with it.