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Slab Leak Detection in Melbourne: How They're Found and Repaired
Slab Leak Detection in Melbourne: How They're Found and Repaired, a Prime Plumbing & Gasfitting plain-English guide to slab leak detection melbourne for Melbourne homeowners. Below we cover what works, what doesn't, and when to call a licensed plumber.
Quick answer: A slab leak is a water pipe leak in pipework that runs under the concrete slab of your home. The signs include warm patches on tile floors (if it's a hot water leak), a continuously running water meter, unexplained mould or damp at the slab edge, hairline cracks in the slab, and the sound of water flowing when no fixtures are open. Slab leaks are located with acoustic detection (microphone on the floor surface) and sometimes tracer gas for harder cases. Repair typically requires either break-out and re-pipe of the leaking section through the slab, or re-route through the wall cavity or roof to avoid breaking up the slab. The right repair depends on the leak location, the slab condition, and what's covering the floor. Pricing varies widely, typically $2,500-$8,000 for a single repair.
What a slab leak actually is
In many Melbourne homes, particularly those built between the 1960s and the 1990s, water supply pipework runs under the concrete slab of the house. The pipes were typically set into the slab at construction, often as copper in older builds or polypipe in some 1980s and later constructions, and emerge at fixture points (kitchen sink, bathroom, laundry).
When one of these buried pipes develops a leak, the water has nowhere to go except into the soil under the slab. Over time it can:
- Saturate the soil bed under the slab
- Cause the slab to crack or settle as soil moves
- Damage flooring above the leak (timber lifts, tiles loosen)
- Rot internal floor finishes and adjacent walls
- Run thousands of litres into the ground each week, costing on your water bill
Slab leaks are particularly tricky because the leak is invisible: there's a slab of concrete in the way, and they're expensive to repair because either the slab has to be broken out, or the pipe has to be rerouted.
How slab leaks happen
Three main causes:
1. Pipe wear from inside
Old copper pipes corrode internally over decades, particularly when water chemistry isn't kind to them (some Melbourne water supplies have been more aggressive on copper than others). Pinholes develop from inside, eventually breaking through to the outside.
2. Slab movement
Concrete slabs move slightly with thermal cycling and with soil movement underneath (especially on Melbourne's reactive clay soils). Copper pipes set into a slab are bonded to the concrete and can't move with it, so cycle stress fractures develop, particularly at fittings or where the pipe makes a bend.
3. Original install issues
Pipes installed without proper sleeving (so the concrete bonds directly to the pipe), bent too sharply, or kinked during the slab pour, these all create future leak points. Some 1970s-1980s installs used poor materials that have since been recognised as unsuitable for in-slab use.
The signs
Hot patches on the floor
If the leak is on the hot water side, the water saturating the slab heats the concrete above the leak. On a tile or vinyl floor, you'll feel a warm patch when you walk barefoot. The patch is usually localised and persistent, different from sun warmth, which is variable.
This is one of the most diagnostic signs of a slab leak. Hot patches on hot side of the leak; no temperature change on the cold side.
Continuously running water meter
Run the meter test described in our underground water leak signs guide: turn off all fixtures and check whether the meter is still moving. A slab leak shows up as a continuous flow on the meter even when no fixture is in use.
Unexplained mould or damp at the slab edge
If you notice mould or persistent damp at the bottom of internal walls (where the wall meets the slab), it can be water from a slab leak wicking up the wall. Particularly visible in laundries, bathrooms, kitchens, anywhere with finishings that show damp readily.
Hairline cracks in the slab
A slab leak that's been running for some time can saturate the soil bed enough to cause the slab to crack, typically thin cracks that run across tile floors and through grout lines. Multiple parallel cracks or a crack pattern that doesn't match expected concrete shrinkage can indicate slab movement caused by saturated soil.
Audible water flow
In a quiet house, particularly at night, you can sometimes hear a faint hissing sound at the floor in the area of the leak. Stand still on different parts of the floor and listen, the leak's sound carries through the slab.
High water bill
The reliable indicator. A slab leak running at moderate rate adds 50-200 L/hour to your usage continuously, easily several thousand dollars/year in unbilled water and growing the longer it runs.
How a plumber locates a slab leak
Step 1: Confirm the leak
Use the meter test to confirm something is leaking, and rule out indoor fixtures (toilets, dishwashers, ice makers, sprinklers). A slow-leaking toilet fill valve looks similar on the meter to a real slab leak, diagnostically different but worth ruling out first.
Step 2: Narrow down hot vs cold
Isolate the hot water unit by closing the hot inlet valve. If the meter stops moving, the leak is on the hot side. If the meter keeps moving with hot isolated, the leak is on the cold side.
Step 3: Acoustic detection
A sensitive microphone is moved across the floor surface, listening for the high-frequency sound of water escaping under pressure. Tile and concrete floors transmit the sound well; carpet over slab is harder but still possible.
The plumber works in a grid pattern across the suspect area, marking where the sound is loudest. With practice, a slab leak can usually be located to within 30-60cm.
Step 4: Pressure mapping (sometimes)
If acoustic isn't conclusive (small leak, noisy environment, heavy carpet), the plumber can isolate sections of the in-slab pipework and test each section with pressure decay. This is more involved and takes longer but locates harder leaks reliably.
Step 5: Tracer gas (occasional)
For very hard-to-find slab leaks, a non-toxic tracer gas can be injected into the pipe; the gas escapes through the leak and rises through the slab to the surface, where a detector picks it up. Used sparingly because it's the most involved method.
Book a slab leak detection
Call 0475 407 670 or send through the contact form. Tell us what symptoms you've seen, hot floor patches, meter still running, mould at the slab edge, and we'll bring the detection gear.
- BPC #103414: Building and Plumbing Commission licence
- 4.8 stars on Google
- Acoustic detection equipment carried on every callout
- Fixed-price written quote before any work
Repair options
Once the leak is located, three main repair paths:
A. Break out and repair (in-place)
Cut a section of the slab over the leak, expose the pipe, repair or replace the leaking section, backfill, re-pour the slab segment. This is the "classic" slab leak repair.
Pros: keeps the existing pipe layout, minimal disruption to the rest of the house plumbing.
Cons: messy, dusty, breaks up flooring above (tile, timber, carpet, all need to be lifted in the work area and either reinstated or replaced), and the patched slab will be visible.
Typical cost: $2,500-$5,000 for a single leak in an accessible area, more if the floor finishes are expensive (engineered timber, designer tile, polished concrete).
B. Re-route the pipe
Run a new pipe through the wall cavity or roof space to bypass the slab section entirely. The original pipe in the slab is abandoned in place. Connections are made above the slab level.
Pros: no slab break-out, no flooring disruption, the new pipe is in an accessible cavity for future maintenance.
Cons: requires good wall/roof cavity access, longer pipe runs, requires neat finishing of any wall cuts and re-painting.
Typical cost: $1,500-$4,000 for a single leak, depending on the length of the re-route and finish work.
C. Whole-house re-pipe
If the slab has multiple suspected leak points or the in-slab pipework is at end of life everywhere, a complete re-pipe through wall and roof cavities is sometimes the better economic decision. Replaces all in-slab pipework with above-slab routing.
Pros: solves the problem permanently, modern pipe (PEX or copper) above slab is much easier to maintain, removes future slab-leak risk.
Cons: substantial cost, takes 2-5 days, multiple wall openings to be patched.
Typical cost: $8,000-$25,000 for a typical single-storey home, depending on size and finish work.
We'll always quote multiple options at the time of detection, and let you choose based on the slab condition, your floor finishes, and your timeline.
For slab leak detection and repair across Melbourne, our burst pipes service covers all three repair paths.
Service area
Prime Plumbing & Gasfitting handles slab leak detection across Melbourne's eastern, south-eastern, inner-east and bayside suburbs. See all suburbs we service →
When to call a licensed plumber
The Victorian Building Authority maintains a plumbing licence search so you can verify your plumber is licensed.
Frequently asked questions
No. Pipe leaks gradually get worse over time as the original failure point erodes further. Some homeowners hope a slab leak might "seal up", it won't. Acting early on a slab leak is much cheaper than waiting until it causes structural damage to the slab itself.
Generally the leak repair itself is classed as maintenance and isn't covered. But the resulting damage: saturated subfloor, ruined flooring, cracked slab, damaged contents, is often covered under home/contents water-damage cover, subject to your policy. Document the leak with photos before any cleanup. Some insurers offer specific underground services policies that include in-slab pipework. Check your policy or call your insurer.
No. A slab leak running for months saturates soil under the foundation, can cause slab cracking and floor heave, and damages flooring above. Repair cost goes up the longer you wait. Locating and repairing early is much cheaper than waiting.
A single in-place slab repair typically takes 1-2 days. A re-route through the wall cavity is usually 1 day. A whole-house re-pipe is 2-5 days. Expect to be without water for periods during the work.
Depends on the repair path and the floor type. Tile: usually 2-4m² of tile around the work area needs to be removed and replaced, matching new tiles to existing can be tricky if the original tile is no longer made. Timber: section of timber over the cut needs to be removed and replaced. Carpet: usually can be lifted and reinstated. Polished concrete: the patch will be visible, sometimes colour-matched, sometimes accepted as is. We'll discuss flooring impact at quote.
The repaired section won't, but other sections of the same in-slab pipe can develop leaks later. If your slab plumbing is 30+ years old and the first leak just appeared, statistically more leaks are likely in the next 5-10 years on the same pipe run. This is why a whole-house re-pipe sometimes makes economic sense rather than fixing leaks one at a time.
The repair is the landlord's responsibility as it's a structural plumbing issue with the property. Document the symptoms (photos of damp patches, water bills if you pay them, hot spots on the floor) and put the request in writing to the agent. If the agent doesn't respond, Consumer Affairs Victoria can advise.
Common enough that we attend several a month. They're particularly common in homes built 1960s-1980s with original copper or polypipe in-slab plumbing that's now reaching end of life. Newer homes (post-2000) tend to have above-slab pipework or better-quality in-slab installs that are still well within their service life.
Before You Book
A quick checklist to share with your plumber when you book:
- When did the issue start?
- Is it isolated to one fixture or multiple areas?
- Are there any visible leaks, smells or unusual sounds?
- Have you turned off the relevant isolation valve?
- Burst pipes Melbourne: slab leak detection, repair, and re-pipe
- Emergency plumber Melbourne: for active major leaks under the slab
