What are the warning signs of a leak under the slab?
Slab leaks hide well, but they leave fingerprints. The classic Queensland giveaways are a warm patch on a tiled or concrete floor where a hot water line runs, a water meter that creeps with everything turned off, a hot water system that seems to run constantly, damp or lifting flooring with no obvious source, mould or a musty smell in one area, and a water bill that has jumped without a change in habits. Outside, a permanently green or soggy strip of lawn beside the slab edge can mark where the leak is escaping. Any two of these together are worth a meter test the same week, because a slab leak never gets cheaper by waiting.
How do you confirm it is under the slab and not somewhere else?
Before anyone talks about concrete, we prove the leak exists and isolate which line owns it. That means the meter test first, then isolating hot from cold and pressure testing each system separately. A pressure drop on the hot side with a warm floor patch is close to a signed confession. We also rule out the cheap suspects: toilet cisterns, irrigation solenoids, the hot water system's relief valve running to waste. In our experience a meaningful share of suspected slab leaks turn out to be one of those, and it takes twenty minutes of testing to avoid a very expensive wrong turn.
How do you pinpoint the exact spot through concrete?
Once the leaking line is confirmed, acoustic detection does the fine work. Pressurised water escaping under a slab produces a distinct hiss and rumble that a ground microphone can hear through 100 mm of concrete, and the signal peaks directly above the breach. For hot lines, thermal imaging maps the warm plume across the floor to shortlist the zone before the microphone confirms it. Where pipe routes are unknown, a pipe locator traces the metal line or a sonde traces plastic. The goal is a chalk mark on the floor, not an opinion, because the difference between opening 300 mm of slab and chasing a guess across a room is measured in thousands of dollars.
Why do pipes leak under Queensland slabs in the first place?
Most slab-era Gold Coast homes ran copper water lines through or under the concrete, and copper in contact with concrete, ash fill or reactive soil can corrode from the outside over decades, particularly at bends where the pipe was worked during installation. Hot lines fail first because heat accelerates the chemistry and the constant expansion and contraction fatigues the metal. Slab movement on our sandy and clay soils adds stress at fixed points, and occasionally the original cause is as simple as a nick from a trowel or a missing sleeve at the slab penetration, laid down fifty years ago and leaking today. None of this reflects on your maintenance. It is materials and decades doing what they do, which is also why a second leak on the same line carries so much weight in our repair-versus-reroute advice.
What are the repair options once it is found?
| Option | What it involves | Typical Gold Coast cost as of 2026 | When it makes sense |
|---|---|---|---|
| Spot repair through the slab | Cut and patch concrete at the marked point, repair the pipe | $1,500 to $4,000 plus, scope confirmed on inspection | One clean breach, sound pipe elsewhere |
| Reroute or overhead bypass | Abandon the slab section, run a new line through walls or roof | Quote on inspection | Second failure on the same line, or hard-to-reach breach |
| Staged or full repipe | Replace the failing pipe system progressively | Quote on inspection | Repeated pinholes, ageing pipe throughout |
We quote all three where they genuinely apply. A second leak on a line that has already failed once shifts our advice toward rerouting, because patching a corroding line under concrete is buying time, not solving the problem, and we would rather say that before you spend the money.
What does the whole process cost?
Detection is $200 to $500 or more as a fixed quoted price, depending on property size and how deep the leak hides. Repairs through the slab start around $1,500 and can exceed $4,000 where the breach sits under finished floors or deep fill, with the exact figure quoted after detection, never sprung on you afterwards. Keep your meter readings and the repair invoice, because concealed leaks on the Gold Coast can qualify for a water bill remission, and the claim needs a licensed plumber's paperwork.
Warm patch on the floor or a meter that will not sit still? Call Hills Plumbing & Gas on 0472 657 042 or book at /services/leak-detection/. QBCC licence 15243081, fixed prices, and we mark the spot before any concrete is touched.