By Cesar · May 19, 2026
The short answer
A slab leak shows up sideways: a warm spot on the floor, damp baseboards, running water you can hear with everything off, a water bill that climbed for no reason. If any of that sounds like your house, do not wait it out.
Common signs of a hidden leak
- Warm or unusually cool spots on a floor
- Moisture along baseboards or under cabinets
- The sound of running water when fixtures are off
- A higher water bill with no change in use
- Flooring that buckles, warps, or smells musty
What to check before calling
If you can, turn off every fixture in the home and watch the water meter. If it’s still moving, water is going somewhere it shouldn’t. That single observation is helpful information for any plumber.
Also note where the moisture or warmth appears and whether it’s spreading. The pattern often points toward the affected line.
Why hidden leaks need careful diagnosis
Slab leaks rarely show themselves where the water actually starts. Water follows the path of least resistance through the slab, framing, and flooring, then surfaces somewhere else entirely.
Opening floors or walls without locating the leak first usually does more damage than it solves. Detection comes first; repair plans come after.
When to shut off water
If water is visibly spreading or you can hear it actively running inside walls or floors, shutting off the main supply is reasonable while you wait. If the leak is small and contained, leave the main on so a plumber can isolate the line on arrival.
What to tell C&F Plumbing
- Where the moisture or warmth is showing up
- How long you’ve noticed it
- Whether the water meter is still moving with everything off
- Whether any flooring or walls feel different
- Photos, if it’s safe to take them
FAQs
- What does a slab leak look like?
- Often it doesn’t look like a leak at all, it shows up as warm spots, baseboard moisture, or sounds of running water with nothing turned on.
- Should I shut off water?
- If water is actively spreading, yes. If the leak is contained, leave the main on so the plumber can isolate the line.
- Can I send a photo?
- Photos help. The contact form supports photo uploads when it’s safe to take one.
- Is a hidden leak urgent?
- A hidden leak that’s spreading or affecting flooring should not wait. The longer it runs, the more it damages.
Still not sure what the problem is?
Tell C&F Plumbing what you’re seeing. A few details can make the next step clearer.