Slab Leaks: Signs, Causes, and What to Do Next

A slab leak occurs when a water pipe running beneath your home's concrete foundation develops a leak. Because the pipe is encased in or under concrete, the leak is invisible — but its effects are not. Slab leaks can waste significant amounts of water, damage flooring, promote mold growth, and in severe cases undermine the foundation itself.

Signs of a Slab Leak

The most common indicator is a warm or hot spot on your floor. If a hot water supply line is leaking under the slab, the escaping hot water heats the concrete above it, creating a noticeable warm area on tile, hardwood, or carpet. Other signs include unexplained increases in your water bill, the sound of running water when all fixtures are off, damp carpet or warped flooring without an obvious source, and cracks in baseboards or walls near the floor level.

What Causes Slab Leaks

The most common cause in Peninsula homes is corrosion in copper supply lines running through or under the slab. Copper reacts with certain soil chemistries and water conditions over time, developing pinhole leaks from the outside in. Poor installation practices — pipes resting directly on gravel or rubbing against concrete — accelerate wear from friction and abrasion.

Ground movement from soil expansion and contraction, seismic activity, or hillside settling can also stress pipes beneath the slab, causing joints to separate or pipes to crack at stress points.

How Slab Leaks Are Found

Professional leak detection specialists use acoustic equipment that amplifies the sound of pressurized water escaping from a pipe, allowing them to pinpoint the leak location through the concrete without guesswork. Electronic leak detection and thermal imaging can also identify moisture concentrations beneath the slab. Accurate localization is critical — it determines whether the repair can be done through a small, targeted access point or requires more extensive work.

Repair Options

Once located, the most common repair approaches are spot repair, reroute, or repipe. Spot repair involves opening the slab at the leak location, repairing the pipe, and patching the concrete. This works well for a single, isolated leak in otherwise healthy pipe.

If the pipe is deteriorated and more leaks are likely, rerouting the line through the wall or ceiling bypasses the under-slab section entirely, eliminating future slab leak risk on that line. For homes with multiple slab leaks or widespread pipe deterioration, a full repipe with rerouted lines is the most comprehensive solution.