Note to readers: This post was updated on July 23, 2026 to reorganize the warning signs more clearly and link to related detection and repair services. We refreshed the details below so the advice reflects how we approach this work today.
Most homes in Southern California sit on concrete slab foundations, which means the water and drain lines run through or underneath that slab rather than through an accessible crawlspace. When one of those pipes corrodes or cracks, the result is a slab leak — and because it’s hidden under the floor, it can go unnoticed until real damage has already happened. Here’s what to watch for.
1. You Hear Running Water With Everything Off
This is usually the first sign homeowners notice. If you can hear water running somewhere in the house but every faucet and appliance is off, there’s a good chance water is escaping into the slab. Shut off your main water supply and call a plumber before it causes more damage.
2. A Musty or Moldy Smell Throughout the Home
Moisture from a slab leak works its way up into flooring, baseboards, and walls, which creates ideal conditions for mold. If you notice a persistent musty smell and can’t find an obvious source, check under sinks, in closets, and along the edges of rooms — and if you still can’t find it, that’s a sign the moisture may be coming from below.
3. Floors or Tiles Buckling or Sinking
Water seeping into the foundation can destabilize sections of slab, causing tile or flooring above it to buckle, crack, or feel uneven underfoot. Catching this early can keep the damage isolated to one area; waiting can let it spread into a much larger foundation repair.
4. Damp Carpet or Flooring With No Obvious Cause
If a section of carpet or flooring is damp and nothing was spilled, don’t ignore it. Peel back a corner to check the padding and subfloor underneath — if that’s wet too, it’s a strong sign of a leak below rather than a surface spill.
5. Water Bills Climbing With No Change in Usage
A sudden jump in your water bill without any change in household habits is a classic leak indicator. Your local water provider can often check for anomalies on their end; if they don’t find anything on the meter side, the leak is likely inside your plumbing.
What to Do If You Suspect a Slab Leak
Don’t wait on this one. Slab leaks that go unaddressed can undermine a home’s foundation and turn into repairs costing thousands of dollars. A plumber can use video camera inspection and leak detection equipment to pinpoint the exact location without guessing where to cut into the slab, which keeps repair costs down. In some cases, trenchless repair methods can fix the line without extensive demolition.
If you’re noticing any of these warning signs, don’t wait for it to get worse — contact Western Rooter & Plumbing. We’ve been diagnosing and repairing slab leaks throughout the San Gabriel Valley for decades.
