Plumbing · 7 min read

What Is a Slab Leak?

A slab leak is one of the most expensive and disruptive plumbing problems a homeowner can face. Here's what it is, how to recognize one early, and what your repair options are.

What Is a Slab Leak?

A slab leak is a leak in the water supply or drain lines that run beneath the concrete slab foundation of a home. Many homes built in the 1960s through 1990s have copper supply lines and cast iron drain lines embedded directly in or under the concrete slab.

Because these pipes are buried under concrete, slab leaks are difficult to detect and can cause significant structural damage, mold growth, and water loss before they're discovered. A slow slab leak can go unnoticed for months while silently eroding the soil beneath your foundation.

Warning Signs of a Slab Leak

Unexplained increase in water bill: If your water usage hasn't changed but your bill has gone up significantly, water may be escaping through a slab leak 24 hours a day.

Sound of running water with no fixtures in use: Turn off all water-using appliances and listen near the floor. A faint hissing or rushing sound can indicate water moving through a cracked pipe under the slab.

Warm spots on the floor: If a hot water line is leaking under the slab, you may feel warm or hot spots on tile or hardwood floors — especially in areas away from heating vents.

Cracks in walls or flooring: Water eroding the soil beneath the slab can cause the foundation to shift, producing cracks in walls, floors, and door frames.

Mold, mildew, or musty smell: Persistent moisture under the slab creates ideal conditions for mold growth. A musty smell that doesn't go away — especially near the floor — can indicate a slab leak.

Wet spots on the floor or in the yard: Water from a slab leak will eventually find a path to the surface — either through the floor or out into the yard near the foundation.

Low water pressure: A significant slab leak can reduce water pressure throughout the house as water escapes before reaching fixtures.

What Causes Slab Leaks?

Corrosion of copper pipes from acidic or aggressive water (common in Maryland well water)
Abrasion from pipes rubbing against concrete or gravel as they expand and contract
High water pressure causing stress on pipe joints
Poor original installation — pipes installed with kinks or improper support
Soil movement or settling beneath the foundation
Age — copper pipes installed before 1970 are reaching end of life

Repair Options

Spot Repair (Break Through the Slab)

$500–$2,000

The most direct approach — jackhammer through the concrete, repair the pipe, and repatch. Best for a single, well-located leak in an otherwise sound pipe system.

Pipe Rerouting

$1,500–$5,000

Run new pipes through the walls and ceiling, bypassing the slab entirely. Avoids breaking concrete and is a good option when the slab pipe is in poor overall condition.

Epoxy Pipe Lining

$1,000–$4,000

A trenchless method that coats the inside of the existing pipe with epoxy, sealing leaks without breaking concrete. Works best for small leaks in accessible pipes.

Whole-House Repiping

$5,000–$15,000

Replace all the plumbing in the home. The most expensive option, but eliminates all aging pipes at once and prevents future slab leaks. Often the right choice for older homes with multiple problem areas.