Breaking concrete to hunt for a leak is the most expensive way to find one — and the least necessary. Professional leak detection exists precisely so the slab gets opened once, in one spot, after the leak's location is already known. Here's how the process actually works, from first test to final mark on the floor.
Step 1: Prove the leak is real
No instruments come out until the loss is confirmed. The technician starts with the meter and a pressure check: with the house quiet, the meter is watched for movement, and the system is checked for pressure decay. These tests answer the first question — is water actually escaping? — and rule out phantom causes like a misread bill or a running appliance.
Step 2: Isolate which line is leaking
A house has hot lines, cold lines, and drain lines, and each gets a different search. By valving off sections and watching the meter or pressure gauge, the technician narrows the field: if the meter stops when the hot-water side is closed, the leak is on a hot line. This isolation step turns a whole-house problem into a single-circuit hunt.
Step 3: Acoustic listening
Pressurized water escaping through a crack makes a distinct sound — a hiss or whoosh that travels through the pipe and the surrounding concrete. Electronic ground microphones and listening discs amplify that sound while filtering out background noise, and the technician maps the loudest point. For slab leaks on copper and other rigid pipe, acoustic listening is usually the primary tool.
Step 4: Thermal imaging
Hot-water leaks warm the slab above them, and infrared cameras see that warmth as a glowing pattern on the floor. The camera sweeps the area the acoustic search flagged, and a matching heat signature confirms the diagnosis. Thermal imaging is also the go-to for leaks behind walls and under flooring where sound is harder to isolate.
Step 5: Tracer gas for stubborn cases
When a leak is too small to hear or the pipe material muffles sound, a safe inert gas can be introduced into the drained line. The gas escapes at the break, rises through the concrete, and is picked up at the surface by a sensitive detector — pinpointing leaks that defeat every other method.
Step 6: Camera inspection for drain lines
Supply lines are pressurized, but drain lines aren't — so acoustic methods don't apply to them. For suspected drain leaks under the slab, a small camera travels the line through an access point and shows cracks, separations, or root intrusion on video, locating the problem by footage markers.
Marking and documenting the find
The visit ends with the leak's position marked directly on the floor or surface, plus a plain-language explanation of what was found and which methods confirmed it. That mark is the whole point: any repair now opens one precise area instead of a trench across the room.
One more honest caveat: no method works in every situation. Extremely small leaks may need the line to be isolated and watched over time, and background noise from nearby equipment can complicate acoustic work. A good technician will tell you when conditions are difficult rather than charging ahead — and may suggest retesting at a quieter hour. The goal is certainty, not speed.
Why pros don't start by breaking concrete
Exploratory demolition is a gamble with your flooring, your foundation, and your budget — and it often misses. A jackhammered hole in the wrong place has to be repaired too, doubling the damage. Instruments cost less than concrete work, and they answer the question before the first cut. If someone proposes breaking the slab before testing, that's the moment to get a second opinion.
After the mark: what happens next
Detection ends where repair begins — and knowing the usual options helps you evaluate quotes calmly. A single accessible leak is often repaired by opening the slab at the mark, fixing the section, and repouring. When lines are broadly corroded, rerouting the line overhead or through walls can beat repeated slab openings. For drain lines, trenchless lining sometimes rehabilitates the pipe from the inside. The key point: none of these decisions should be made before the leak is located. A contractor who wants to commit to a repair method before detection is selling a solution to an unlocated problem. Get the mark first; choose the fix second.
Suspect a leak under your slab? Professional slab leak detection finds it first and breaks concrete never — or once, in exactly the right place. Call +1 843-936-8115 — open 24 hours.