A slab leak is a water line leaking under your home's concrete foundation. It's expensive because it's hidden: the first signs are usually a water bill that jumped, a warm spot on the floor, or the faint sound of running water when everything is off.
Before paying a pro $150–$400 for electronic leak detection, run this test. Your water meter measures every gallon that enters the house — if the meter moves while nothing is using water, water is going somewhere. The test takes five minutes of work and about two hours of waiting.
Stop all water use in the house: no faucets, showers, laundry, or dishwasher. Switch off the ice maker and any irrigation system, and don't flush toilets during the test — a single flush moves the meter and ruins the reading.
The meter is usually in a covered box at the curb or near the street. Most meters have a small flow indicator — a spinning dial, triangle, or digital readout that reacts to even tiny flows. If it's spinning with everything off, you already have your answer: water is moving.
Take a photo of the meter reading and note the leak indicator's position. A photo beats memory — you're looking for a small change, and the dial makes it easy to fool yourself.
Leave the house or run the test overnight, with zero water use in between. Slow pinhole leaks move the meter slowly, so a longer window catches leaks a 30-minute test would miss.
If the reading changed, there's a leak. To find whether it's in the house or the yard line, close the house's main shut-off valve and watch the meter again: still moving means the leak is in the service line between the meter and the house; stopped means the leak is inside or under the slab. Before concluding it's the slab, rule out the two great mimics — a running toilet and an irrigation leak each waste hundreds of gallons a day and cost far less to fix.
If the test says leak: professional electronic detection typically runs $150–$400 and pinpoints the spot before anyone cuts concrete. A spot repair after detection typically runs $1,500–$4,000; a full repipe to bypass the slab runs $4,000–$12,000. Get the detection report in writing before authorizing demolition, and call your insurer early — slab-leak *damage* is often covered even when the pipe repair isn't.
Warm spots on the floor, the sound of running water with everything off, cracks appearing in floors or walls, or a sudden water-bill spike — book detection now. Slab leaks erode the soil under your foundation, so weeks of 'watching it' can turn a pipe repair into a foundation problem.
Very — the meter measures all water entering the property, so any movement with zero usage means a leak exists somewhere. The shut-off isolation step then separates a house/slab leak from a yard-line leak. What the test can't do is locate the leak; that's what paid detection is for.
A short test can. Pinhole leaks may move the meter only slightly per hour — run the test overnight (6–8 hours) for a conclusive result, and watch the low-flow indicator, which reacts before the main digits change.
Often partially: many policies cover the resulting water damage and the cost of accessing the pipe, but not the pipe repair itself. Document early — photos of the meter readings and the bill spike are exactly what a claim wants.
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