Slab Leak Repair

What a slab leak is

A slab leak is a leak in a water line that runs underneath your home's concrete foundation. Most homes in the San Fernando Valley and across Los Angeles are slab-on-grade, meaning the copper supply pipes were poured into or run directly beneath a single slab of concrete. When one of those pipes develops a pinhole — usually after 25-40 years for copper — the water has nowhere to go but into the slab, the soil, and eventually up through the floor or out along a baseboard.

The leak is hidden, so it runs for weeks or months. The water bill creeps up, a section of floor stays warm, paint starts to bubble — and by the time it is obvious, the leak has been wetting the foundation the whole time. The fix is not hard once you know exactly where it is; the cost lives in finding it without guessing.

Signs of a slab leak

A warm spot on the floor is the most reliable sign of a hot-water slab leak. The escaping hot water heats the concrete from below, and you can often feel it barefoot on tile or vinyl before the house warms up in the morning. A cold-side leak will not warm the floor, so the absence of a warm spot does not rule a slab leak out.

A water bill that jumped without a change in use is a classic tell — a pinhole under the slab leaks 24 hours a day, so the bill climbs by thousands of gallons with no new irrigation, appliance, or houseguests. To confirm, stand by the water meter at the curb with every fixture and irrigation valve closed: if the small leak-indicator dial is turning, or you hear faint running water inside a quiet house, the supply line is losing water.

Low water pressure throughout the house points to a slab leak too, because the leak bleeds pressure off the supply side. If flow has gone weak at every fixture at once — not just one faucet — a slab leak is a likely cause, alongside a failing pressure-reducing valve. Cracks in flooring or drywall, a musty smell, or mold along a baseboard round out the list: water moving through the slab lifts the concrete and feeds mold even when there is no visible drip.

How we find it before we cut

Cutting blind into a slab is expensive and rarely lands on the leak the first time, so we never do it. We start with a pressure test: with every fixture closed, we isolate the supply line and watch for pressure drop. If it will not hold, the leak is on the pressurized supply side and a slab leak is in play.

From there we use ground microphones to listen for the high-frequency hiss of water escaping under the slab, gridding the suspected area and triangulating until we have the spot within a few inches. On hot-side leaks we add thermal imaging — the warmed concrete shows up as a clear pattern through the camera. You get a marked spot on the floor and a written report before any concrete comes out, which keeps the patching to a minimum.

Repair options and pricing guidance

Spot repair is the most common fix when the leak is in one location and the rest of the line is sound. We open a small section of slab, cut out the failed pipe, splice in new copper, pressure-test it, and restore the concrete. Typical Valley spot repair runs $1,200-$2,800 depending on access and finished-floor type.

A reroute abandons the failed pipe entirely and runs a new line above the slab — through the attic, walls, or along the exterior — instead of repairing under concrete. It is often the smarter long-term move on an older home where the same pipe is likely to spring another pinhole nearby. Reroutes typically run $2,500-$5,500. If the whole system is at end of life, a full repipe ($7,500-$18,000+) puts the leak problem behind you for good.

Epoxy pipe lining is an option when a line has several pinholes but is otherwise intact and accessible. We clean the inside of the pipe and coat it with a structural epoxy that seals the existing pinholes and slows future corrosion — no slab demolition. We will tell you honestly which of these fits your pipe, your foundation, and your budget; there is no single right answer for every house.