5 Warning Signs of a Slab Leak in Your Gilbert Home

Most homes across Gilbert and the East Valley are built slab-on-grade — the concrete foundation sits directly on the ground, with the home's water supply and drain lines routed through or under that slab. It's a durable, standard building method for Arizona's soil and climate, but it has one real downside: when a pipe under the slab starts leaking, there's no visible drip, no water stain on a ceiling, nothing obvious to point you to the problem. The leak can run for weeks, quietly soaking into the ground or working its way up through the concrete, before it becomes impossible to ignore. Here are the five signs that usually show up first.

1. A water bill that jumps for no clear reason

If your usage habits haven't changed but your water bill climbs noticeably month over month, a slab leak is one of the most common explanations — especially if you've already ruled out an obvious running toilet or a sprinkler system malfunction. A pipe leaking under the slab can lose water continuously, 24 hours a day, without anyone noticing a drop on the surface.

2. The sound of running water when everything is off

If you can hear a faint hissing or running-water sound coming from the floor when every fixture in the house is off, that's a strong indicator of a pressurized supply line leaking under the slab. It's often most noticeable at night when the house is quiet — try listening near baseboards or in a closet that backs up to a plumbing wall.

3. Warm or damp spots on the flooring

If the leaking line is on the hot water side, you may notice one area of tile, carpet, or flooring that feels noticeably warmer than the rest of the room, sometimes even before any moisture is visible. On tile or concrete floors, dampness that returns no matter how often it's wiped up is another version of the same sign.

4. Mold, mildew smell, or unexplained humidity

Moisture trapped under flooring or inside a slab doesn't need to reach the surface to create a mildew smell in the room above it. If a specific room has developed a musty odor, unexplained humidity, or flooring that's starting to warp, cup, or lift at the seams, water intrusion from below is a common cause — particularly in older homes where original supply lines are reaching the end of their service life.

5. Cracks in flooring, drywall, or the foundation itself

A long-running slab leak can erode the soil underneath the foundation, and as that support shifts, cracks can appear in tile grout lines, baseboards, drywall corners near the floor, or the slab itself. This is typically a later-stage sign — by the time cracking shows up, the leak has usually been running long enough that acting quickly matters.

How professional leak detection works

The days of guessing where a slab leak is by breaking up sections of concrete are largely over. Modern leak detection uses acoustic listening equipment to pinpoint the sound signature of pressurized water escaping a pipe, sometimes paired with thermal imaging to spot temperature differences in the flooring, and video pipe inspection where access allows. The goal is always the same: locate the leak as precisely as possible before any repair work starts, so the fix is targeted instead of exploratory.

What happens after the leak is found

Once the location and severity are confirmed, the repair path depends on what's practical for that specific line — a small access point and spot repair, rerouting the line through a wall or ceiling to bypass the slab entirely, or in some cases relining the existing pipe. A good diagnostic should always come with a clear explanation of why a given repair method is being recommended over the alternatives, not just a number.