How to Find a Slab Leak

Finding a slab leak takes two stages. Stage 1 is a DIY water meter test: turn off every tap and appliance, then watch your meter's leak indicator for 15–20 minutes. If it keeps moving, water is escaping somewhere in the system. Stage 2 is professional slab leak detection: pressure testing to identify which line is failing, tracing the pipe's actual route under the slab, then acoustic listening and thermal imaging to pinpoint the leak — confirmed by a second method before any concrete is opened. If the meter test shows nothing but you still have dampness, odors, or soggy spots, suspect a drain-side leak: drains are not pressurized, so the meter cannot see them, and a camera inspection is how those are found.

This is the one test every homeowner can run, and it is the same test a technician will run first. It tells you whether water is escaping — not where.

1. Turn off everything that uses water. Every tap, shower, toilet fill, dishwasher, washing machine, and irrigation system. A running ice maker or a toilet that refills will fake a leak on the meter.
2. Find your water meter and note the reading. Most Edmond meters have a small leak indicator — a triangle or star-shaped dial that spins with even tiny flow. Note the main reading too.
3. Wait 15–20 minutes without using any water. Then check the meter again. If the leak indicator is still moving, or the reading has climbed, water is leaving the system somewhere between the meter and your fixtures.
4. Run the shutoff trick to narrow the search. Close the main shutoff valve at the house (not at the meter). If the meter stops, the leak is between the house valve and your fixtures — the under-slab zone. If the meter keeps moving with the house valve closed, the leak is in the yard line between the meter and the house, which is a water leak detection job outside the slab, not under it.

What the Meter Test Can't Tell You

Two limits matter. First, the test confirms a leak but says nothing about which line or where — a pinhole in a hot-water line and a split in a cold line look identical on the meter. Second, it is blind to drain-side leaks. Drains only carry water when fixtures empty into them, so they never move the meter. If your meter test is clean but you have musty odors along a baseboard, a damp patch that never dries, or a soggy spot against the foundation, the next step is not another meter test — it is a camera inspection of the drain lines (see Stage 2).

Once a leak is confirmed, a detection visit follows a sequence. Each step narrows the search area before anyone touches the concrete, and a good technician will not mark a cut spot on one method alone.

1. Pressure-test to identify the failing line. Individual supply lines are isolated and pressurized with air or water, then watched for pressure drop. This separates a supply leak from a drain leak and a hot-side leak from a cold-side one — and it can cut the search area from the whole house to one run of pipe.
2. Trace the pipe's actual route. A line tracer maps where the pipes really run under the slab. As-built drawings are often missing or wrong, and this step is what keeps a crew from cutting in the wrong room.
3. Listen with acoustic equipment. Ground microphones and amplified listening discs pick up the hiss of pressurized water escaping a pipe. Under concrete that sound has a distinct signature, and the technician sweeps a grid across the suspected zone until the signal peaks. Hard flooring transmits sound well; carpet and thick pad make this harder.
4. Confirm with thermal imaging or electronic readings. A thermal camera sees the warm plume that escaping hot water creates on the floor above it — fast and decisive on hot-side leaks, much weaker on cold-side ones, so it is never used alone. Electronic leak detection reads moisture and signal variation through the slab as a second opinion.
5. Use tracer gas where acoustics struggle. On plastic lines and low-pressure situations, the line is drained, charged with a non-flammable forming gas (typically 5% hydrogen, 95% nitrogen), and a gas-sensitive detector at the surface finds where the tiny gas molecules migrate up through the slab. Slower to set up, hard to argue with.
6. Camera-inspect drain lines. A drain problem is confirmed visually: a camera on a flexible cable is fed through a cleanout, and a locating transmitter on the camera head marks the exact depth and position of the defect from above the slab. A hydrostatic test — plugging the line and filling it with water to see if it holds — confirms a drain leak that the camera alone cannot prove.

Why Two Methods Before Cutting

No single detection method is right for every leak. Acoustics are weak on plastic pipe and under thick carpet. Thermal imaging is weak on cold-side leaks. A camera only sees drain lines. Confirming with a second method is what turns "somewhere in this room" into a spot worth opening — and it is the difference between a repair that opens a few square feet and one that chases a leak across the floor.

Edmond homes sit on expansive clay soil that swells when wet and shrinks when dry. Water escaping under the slab does not just sit there — it erodes the compacted soil supporting the foundation, and as that support washes out, sections of slab can settle and crack. A leak located this week is a plumbing repair; the same leak located months from now can become a foundation repair problem on top of it. That is also why the meter test is worth doing the moment a bill spikes or a warm spot appears, rather than waiting to see whether it gets worse — it will not get better on its own.

If you are in an established neighborhood like Coffee Creek or along the Danforth Corridor, where decades-old copper lines meet the same clay soil, the odds tilt further toward acting on the first clue rather than the third.

The meter test is where DIY ends and equipment begins. Call for professional detection when:

• The meter test confirms a leak, or the shutoff trick points under the slab
• The meter test is clean but drain-side symptoms persist (odors, damp spots, slow drains)
• You can hear running water with everything off but cannot tell where it is coming from
• A warm floor patch, damp flooring, or a new crack has appeared and you want the spot marked before it spreads

Treat it as an emergency — shut off the main supply and call the same day — if you have standing water indoors, a floor that is hot across a wide area, or the sound of rushing water under the floor.

Location is the decision point, not the end of the job. Once the spot is marked, the repair options open up: a spot repair through a small opening, pipe rerouting around the failed section, or a full repipe if the system is aging out section by section. (Repair options are covered in depth in our guide to how to fix a slab leak.) What location buys you is a repair priced on a known problem instead of a guessed one — and a floor that stays mostly intact.

When you call Edmond Slab Leak Pros at (572) 205-4235, tell us what the meter test showed and which rooms show signs. We connect you with an independent local plumbing provider who runs the full detection sequence — usually in a single visit — and marks the leak before anyone talks about opening concrete.