Slab Leaks: How They're Found Before Anyone Cuts Concrete

Most homes here sit on a concrete slab, with supply lines running beneath it or through the walls above. A leak under the slab rarely shows itself as a visible drip, which is exactly why it gets expensive.

What it feels like

• A warm patch on a tile or slab floor — that's a hot-water line.
• The sound of running water with every fixture closed.
• A water bill that jumped with no change in use.
• Flooring that buckles or a musty smell in one area.

How location actually works

The first step is confirming there's a supply leak at all: isolate the system at the main and watch whether pressure holds. If it drops, the leak is on the supply side. If it holds, the problem is somewhere else — a drain, irrigation, a pool line or the roof — and cutting the slab would have been a wasted day.

From there, acoustic listening equipment tracks the sound of escaping water through the slab, and line tracing establishes the pipe's route and depth. Between the two, the leak gets marked to within a small area.

Repair options

Sometimes direct access through a small opening in the slab is the cleanest fix. Often it's better to abandon the failed section and reroute the run overhead through the attic and down a wall, which avoids the slab entirely and gives you accessible pipe in future. Which one is right depends on the pipe's condition, its depth and what's above it.

The order matters: confirm, locate, then open. Anyone proposing to cut concrete before locating is guessing with your floor.

How can I check for a slab leak myself?

Turn off every faucet, appliance and the irrigation system, then look at the water meter. If the leak indicator — usually a small triangle or dial — is still moving, water is going somewhere. Note the reading, wait an hour without using any water, and check again. That tells you there's a leak on the supply side; it doesn't tell you where.

Why do slab leaks happen in older homes?

Many homes built in the second half of the last century have copper supply lines under or through the slab. Over time, hard water, abrasion where pipe touches concrete, and small movements in the slab wear through the pipe wall. Hot-water lines tend to fail first, because heating and cooling adds stress with every use.

What should I do while I wait for a plumber?

• If you hear water running or find a warm spot, close the main shutoff.
• If it's a hot-water line, turn off the water heater and close its cold supply valve so the line stops refilling.
• Photograph the floor, the meter reading and anything damaged.

Every High Seas service call includes a whole-home plumbing inspection, so the rest of the supply system gets checked while the leak is being located.