The wet spot is not necessarily where the pipe is broken. Water travels under concrete before surfacing. The correct process proves which line is leaking first -- then narrows the location before any concrete is cut.
Learn the H.U.N.T.E.R. Method → Free Report AppA pool leak under concrete is found by first proving which plumbing line or area is losing water, mapping the pipe route, then using acoustic listening, trace gas, or both to narrow the most likely leak location before concrete is cut. Wet spots, visible dampness, and efflorescence show where water surfaced -- not where the pipe broke. Multiple layers of evidence should support the repair access decision, not a single weak signal or surface clue.
Do not cut concrete from a wet spot alone. Do not cut concrete from one weak pressure test. Prove the line, map the route, narrow the location with locating tools, then plan the access based on the convergence of evidence.
Water escaping from an underground pipe does not always rise straight up. It follows the path of least resistance -- and under a pool deck, there are many paths that are easier than traveling straight through compacted concrete.
The wet area on the surface may be several feet -- or more -- from the actual pipe break. A technician who cuts where the deck is wet is guessing, not diagnosing.
Confirm abnormal water loss and gather customer history
Compare pump-on vs. pump-off water-loss behavior
Inspect equipment, valves, waste line, and visible plumbing
Inspect pool shell, skimmers, lights, returns, main drain, and fittings with dye testing
Isolate and pressure test the suspected plumbing line -- verify the setup before blaming the pipe
Map the pipe route -- know where the line runs before listening or sniffing
Use acoustic listening, trace gas, or both along the mapped pipe route
Mark the area with the strongest, most repeatable evidence
Explain confidence level and limitations clearly before recommending access
Verify after repair -- pressure test the repaired line before backfilling
Each tool has limits. Thermal imaging may show moisture patterns. Moisture meters may show damp areas. Ground penetrating radar may show voids or utility routes. None of these replace pressure testing, pipe route mapping, acoustic listening, and trace gas as a coordinated process.
The strongest under-concrete repair recommendation comes when multiple evidence types point to the same area -- a confirmed pressure-test failure, a mapped pipe route, a repeatable acoustic signal, and a consistent trace gas reading that agree on the same location. When they disagree, the technician should slow down and investigate why before recommending concrete access.
Customer history -- pump-on vs. pump-off loss pattern, wet areas in the yard, prior repairs, and autofill behavior -- directs which circuit to investigate and where to focus the search.
Map the full plumbing system before any locating begins. Know which lines run under which parts of the deck. Understand what connects to what so the pressure test isolates the correct circuit.
Visual inspection, dye testing, and equipment inspection narrow the most likely leak zone before pressure testing. Pressure testing narrows to the specific circuit before locating tools are deployed.
Pressure test the confirmed suspect line. Verify the setup. Map the pipe route. Then apply acoustic and trace gas tools along the mapped path -- not randomly across the deck.
Document the pressure result, the pipe route, the acoustic signal quality and location, and the trace gas readings. Multiple clues pointing to the same area are stronger evidence than any single tool result.
Recommend the most likely access area based on the convergence of evidence. State confidence level and limitations clearly. Verify after repair before backfilling and deck restoration.
Can a pool leak under concrete be found without cutting the deck?
Often, yes. Pressure testing, pipe locating, acoustic listening, and trace gas can narrow the most likely leak area before any concrete is removed. The goal is to make the access decision based on evidence rather than guessing -- which reduces the chance of opening the wrong area.
Does a wet spot on the deck show where the pipe is broken?
Not reliably. Water under concrete follows the path of least resistance -- pipe trenches, sand beds, gravel, expansion joints, and voids. The wet surface area may be several feet away from the actual pipe break.
Does a failed pressure test show the exact leak location?
No. A failed pressure test confirms that the tested circuit is losing pressure. The exact location requires further locating work -- acoustic listening, pipe route mapping, trace gas, or a combination.
Which is better for under-concrete leaks -- acoustic or trace gas?
It depends on the site. Acoustic works well when the leak creates a clear sound signal and background noise is low. Trace gas may help when the leak is quiet, the pipe is deep, or the site is noisy. On difficult jobs, using both and comparing the results provides stronger evidence.
Jeff David is the founder of Leak Business Academy, LLC and Leak and Subsurface Locators, LLC. He is a licensed pool contractor in Florida and an FSPA Palm Beach board member. Under-concrete locating is the highest-stakes part of pool leak detection -- a wrong cut costs the homeowner unnecessary demolition and repair. The process described on this page is the sequence used at Leak and Subsurface Locators: prove the line, map the route, narrow the location, confirm with multiple evidence types, then plan the access.
LBA training covers pressure testing, pipe route mapping, acoustic locating, trace gas, and evidence-based repair access planning -- all in the correct sequence.
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