A slab leak happens when a pressurized water line running under or through your concrete foundation springs a leak. In most Arizona homes, the supply lines are copper, and they're often poured directly into the slab. When one fails, water has nowhere to go but into the concrete and the soil beneath it, which is why the symptoms can stay subtle for weeks before they turn obvious and expensive.
Warm or hot spots on the floor are one of the clearest signs, and they point specifically to a leak on the hot-water line. If you walk barefoot across tile and feel a patch that's noticeably warmer than the rest, that's heated water spreading through the slab. Pair that with a water bill that jumps with no change in your habits, and you've got two independent symptoms pointing at the same problem.
Listen when the house is quiet and every fixture is off. If you hear a faint hiss or the sound of running water, walk to your water meter and watch the low-flow indicator. If it's spinning with everything shut off, water is escaping somewhere in the system. A drop in pressure across the whole house often comes with it, because the leak is bleeding off pressure that should be reaching your fixtures.
Cracks in flooring or drywall, doors that suddenly stick, and a musty or mildew smell that won't quit all point to moisture moving through the structure. As water saturates the soil under the slab, the foundation can shift a little, and that movement shows up as hairline cracks in tile grout or wall corners. The smell comes from moisture wicking up into baseboards, carpet pad, and cabinetry where mold takes hold.
Arizona homes are especially prone to slab leaks for a few specific reasons. Our hard water, often 12 to 20-plus grains per gallon, drives pinhole corrosion in copper from the inside out. Expansive desert soils swell and contract with seasonal moisture, stressing the pipes. And in older Del Webb and Valley communities, those copper lines have been sitting in the slab for decades. It's rarely one cause. It's the combination.
If you suspect a slab leak, the right move is electronic leak detection, not a jackhammer. We use acoustic listening equipment and pressure testing to pinpoint the leak to within a small area before opening any concrete. Blind digging means tearing up far more floor than necessary and still risking a miss. Locating it first means a smaller, smarter repair, and a clear choice between a spot fix, a reroute, or a repipe.