Slab Leak

A slab leak is a water leak in plumbing pipes that run through, under, or embedded in the concrete slab foundation of a home. Unlike leaks in walls or under sinks, slab leaks are hidden — homeowners often don't realize a leak exists until the water bill spikes, the floor warms (hot-water leak), the floor warps, or mold appears.

Why do slab leaks happen?

In homes built between roughly 1960 and 1990 in the Sun Belt (Phoenix, Houston, Dallas, Atlanta, Tampa), copper supply lines were routed through the slab. Over 30–60 years, pinhole corrosion (especially in hard water) creates leaks. Hot-water lines fail more often than cold (heat accelerates corrosion).

What are the symptoms of a slab leak?

• Unexplained water bill increase
• Warm spots on the floor (hot-water slab leak)
• Sound of running water with all fixtures off
• Mold or mildew smell near the floor
• Cracks in the slab or warping of flooring
• Water seeping through concrete

How is a slab leak located?

Locating comes before breaking any concrete, and it is done in stages. The system is isolated and pressure-tested to establish that the loss is on the supply side and whether it is the hot or the cold line. Acoustic listening equipment then tracks the sound of escaping water through the slab, and thermal imaging narrows a hot-water leak by finding the warm path. Where the reading is ambiguous, tracer gas is introduced into the drained line and picked up at the surface as it permeates the concrete. A licensed plumber should be able to mark the spot within a foot or so before any saw touches the floor.

What are the repair options for a slab leak?

Spot repair (jackhammer the slab, replace the leaking section, $800–$2,500), reroute (abandon the leaking section in the slab, run new line through the attic or walls, $1,500–$4,000), or full repipe ($4,500–$15,000 — recommended if the home has had 2+ slab leaks).