Most hidden leaks show up on a water bill long before they show up anywhere in the house. The quarter comes in high, nothing looks wet, and the extra guests over Christmas get the blame. Then the next bill lands.
If you're working out how to find a water leak you can't see, start at the meter. Turn everything off, read the smallest dial and give it a full five minutes. Any movement means water is escaping. Check the toilets next, because a silent cistern is the usual culprit behind an unexplained high water bill. Once they're cleared and the dial still creeps, the leak is in the pipework. In Melbourne, a hidden water leak most often turns up on the underground stretch between the meter and the house. Pinning down the exact spot from there is a job for acoustic and thermal detection gear.
Key takeaways
- A water leak test at the meter needs at least five minutes with every tap and appliance off. A glance won't catch a slow leak.
- Toilets are the usual suspect, and a dye test in the cistern costs next to nothing.
- Shut the main stop tap at the house and watch the meter. If it keeps moving, the leak is on the underground service pipe.
- Hidden water leaks inside walls and ceilings tend to show within days, but a water leak underground can run for months without a trace.
- The more precisely a leak is located, the smaller the hole needed to fix it.
How do you check for water leaks using the water meter?
Before you work out how to find a water leak, prove there is one. Turn off every tap and water-using appliance, note the reading on the meter's smallest dial and check it again after at least five minutes. If the dial has moved, you have a leak.
A few seconds of watching tells you very little. A slow leak running at 18 to 20 litres an hour barely nudges the dial, and plenty of people glance at it, see nothing and walk away satisfied.
The water leak test that settles it is an overnight one. Take a reading once the household has gone to bed, check that the dishwasher and washing machine aren't on delay timers, and read the meter again before anyone gets up. Repeat it the next night. A leak shows the same steady rate both times. When the numbers jump around, something on the property is drawing water on its own schedule, usually irrigation or a pool top-up.
Your bill gives you a second reference point. Melbourne water bills show your average daily use, so compare yours with a neighbour whose household is a similar size. Using two or three times their figure is a strong sign.
Don't wait for a second high bill to confirm the first.
Why is water leaking into the toilet bowl when nobody has flushed?
A worn flush valve seal or a faulty inlet valve lets water run from the cistern into the bowl around the clock. The leak makes little or no noise, which is why toilets sit behind so many unexplained bills.
The numbers show why nobody notices. Twenty litres an hour works out to about 5 millilitres a second, a thin film down the back of the bowl that disappears against white porcelain.
A dye test for water leaks removes the guesswork. Put a few drops of food colouring or a dye tablet into the cistern (the tank at the back, not the bowl), leave the toilet alone for about 20 minutes and then look. Colour in the bowl means the seal isn't holding. For a quicker read, shine a torch at the waterline. Still water sits dead flat, so any ripple means water is coming through.
In a house with more than one toilet, turn off each cistern's stop tap and take a meter reading. Then open them one at a time. If a cistern starts refilling without being flushed, that toilet is your leak. The repair is usually a new flush valve seal or inlet valve, which is a small job compared with a quarter's worth of wasted water.
How do you find a water leak before calling a plumber?
Shut off one part of the system at a time and read the meter after each change. The hot water system and the main stop tap at the house tell you the most. Every area you rule out is ground a detection technician no longer has to cover.
Start at the hot water unit. Close the cold isolation valve on its inlet and read the meter again. The one valve takes the unit and every hot pipe in the house out of the test, so the search area roughly halves. If the meter stops, look at the temperature and pressure relief valve on your hot water unit and the drain line below it. A steady discharge from that valve needs a licensed plumber, because adjusting or replacing it isn't safe DIY work.
Next, find the main stop tap. Plenty of houses have one where the supply enters the building, separate from the tap at the meter. If the dial keeps turning with that tap closed, the leak is on the underground service pipe between the meter and the house. If it stops, you're looking indoors.
Before blaming a pipe, check anything that runs by itself. An irrigation solenoid stuck open will keep a meter ticking all night. So will the mains top-up on a pool or rainwater tank with a faulty float.
For exposed pipework under sinks and behind the washing machine, press a dry tissue against each joint. A few drops leave a mark you won't miss.
What are the signs of a water leak inside a wall or ceiling?
A water leak inside a wall usually gives itself away within days. A pressurised pipe losing 20 litres an hour has nowhere to hide in plasterboard.
Look for:
- Paint bubbling or flaking low on the wall
- Skirting boards that swell or pull away
- Carpet or a floating floor that feels damp or starts lifting
- A musty smell in one room that airing out doesn't fix
- Wet-area tiles that sound hollow when tapped
So if your meter says there's a leak, but nothing has marked after a week or so, the leak is almost certainly underground.
A frequent cause inside walls is a screw or nail driven through a pipe when a shelf or TV bracket went up, sometimes years earlier. The pipe can stay sealed around the fixing until the metal corrodes or shifts. That explains the leak that appears in a wall nobody has touched in a long time.
Water leaking from the ceiling is harder to trace. An upstairs bathroom or a hot water unit in the roof space is the usual source, and water runs along joists before it drips, so the stain often sits well away from the leak.
How to find a water leak underground or under a slab
A water leak underground rarely shows at the surface. You confirm it at the meter by elimination, and a technician then locates it with detection equipment. Under-slab leaks get a pressure test before anyone lifts a tile.
In Melbourne, the water corporation owns the meter, and you own the service pipe on the house side of it. The pipe runs from the front boundary, often under a driveway or garden bed, and a leak there can go completely unseen. One was found about 45 centimetres from the meter under a concrete driveway, with the surface above it bone dry.
Reactive clay is behind a lot of these leaks. Across Melbourne's north and west, the ground swells through winter and shrinks hard in a dry summer, and that movement works rigid joints on older copper or galvanised lines loose year after year. Roots from street trees and mature gums then find the weak joints. Every so often the pipe also turns out to be shallower than the plans show, or in a different spot. Nobody finds that out until the digging starts.
Weather can also mask the evidence. After a wet spell, a leak can hide for months because saturated ground all looks the same. A dry summer does the opposite. If a strip of lawn along the line from the meter stays green in February while the rest browns off, that strip deserves a closer look.
If your home sits on stumps, as many weatherboards and Californian bungalows in the inner north and east do, open the subfloor hatch with a torch. A leaking pipe under the house tends to leave damp soil, pooling or a tide mark on the stumps.
Slab homes need a different approach. Newer builds run much of their pipework in or beneath the concrete, and the reliable way to confirm a water leak under a slab is a pressure test. The plumber isolates each section of pipe, pressurises it and watches the gauge for a drop. Detection then narrows the location so only a small section of floor comes up.
Can plumbers detect leaks behind walls without cutting them open?
Yes. Most hidden water leaks can be found before anything is opened up. Water leak detection uses acoustic listening gear and thermal imaging, with tracer gas for harder cases, to pinpoint the spot through plaster, tiles or concrete.
Acoustic leak detection relies on sound. Water escaping under pressure makes a distinct hiss, and ground microphones pick it up through concrete and soil. Copper carries that noise well. Plastic pipe, common in newer Melbourne homes, deadens it, so on plastic lines the technician often switches to tracer gas. This is a safe hydrogen and nitrogen mix pushed into the pipe and picked up where it escapes. Tracer gas takes longer, so if a detection visit on a newer home runs past what you expected, that's usually why.
Thermal imaging works best on hot lines. A water leak inside a wall or slab shows up on the camera as a warm bloom spreading from the pipe.
Detection and repair are often separate jobs, and sometimes separate businesses. When you book, ask whether the same team handles the fix.
Location accuracy has a direct effect on what the repair costs. A leak pinned to a small area means a small hole in the driveway or a couple of tiles lifted. Without that precision, the hole gets bigger, and the dig is nearly always the most expensive part of the job.
Very small leaks can fall below what the equipment picks up. When that happens, the culprit is usually a toilet or a dripping fixture, so run the checks above first. Repairs we complete after detection carry the Jacksons lifetime workmanship guarantee. That guarantee counts most on a joint rejoined under a slab or driveway, where you'll never see it again.
Who pays for hidden water leak detection and repairs?
Depending on where the leak is, your insurer, owners corporation, builder or water corporation may cover part of the cost. Check before you book.
Some home insurance policies pay to locate the source of a leak even when they won't cover the worn pipe. Read the product disclosure statement or ring your insurer first.
In a unit or townhouse, leaks in common property can fall to the owners corporation, and that can include the slab and shared service lines. The plan of subdivision shows where your lot boundary sits.
In a newer home, call the builder before anyone else. Victoria's Domestic Building Contracts Act 1995 builds statutory warranties into every domestic building contract. The Building Act 1993 generally allows claims for defective building work up to 10 years from the occupancy permit. Consumer Affairs Victoria sets out the details, and it's a more reliable source than a forum thread.
Yarra Valley Water, South East Water and Greater Western Water each have a process for concealed leaks. Once a licensed plumber has fixed the leak, it can reduce the charge for the water you lost. Ask your plumber for an invoice that states where the leak was.
Be wary of anyone who asks for a large fee before they've seen the property, or quotes an hourly figure without a clear scope of work. A good detection visit ends with the leak marked and a plain explanation of why the pipe failed and what the fix involves. Nobody should be using it to sell you something else. You can confirm any plumber's licence on the Building and Plumbing Commission's register.
What should you do if you're losing a lot of water right now?
Turn the water off at the meter between uses, and fill a few buckets so the toilets can still be flushed until a plumber arrives.
The meter sits near the front boundary on most Melbourne properties, sometimes under a small lid. Turn its tap clockwise until it stops, or a quarter turn if it has a lever handle. If water is leaking from the ceiling near a light fitting, switch the power off at the switchboard and keep clear of that room.
Do I need to be home for leak detection?
Usually. In a rental, the property manager can arrange access with the tenant.
If the meter is still moving after you've ruled out the toilets and the hot water system, the leak needs locating properly. Book a leak detection visit with Jacksons Local Plumbing, and we'll mark exactly where it is and quote the repair before any digging starts.
FAQs
Who is responsible for a leak between the water meter and the house in Victoria?
The property owner. The water corporation looks after the meter and the pipes on the street side of it, and everything downstream of the meter is yours to repair.
Can thermal imaging find a cold water leak?
Sometimes. A cold line gives the camera far less to work with than a hot one. Still, a wet patch of wall can read cooler than the dry plaster around it as the moisture evaporates. On cold lines, a detector will usually rely on acoustic gear or tracer gas and treat the thermal image as a supporting clue.
Will a hidden water leak damage the house if I leave it?
Given time, yes. Inside walls, the damage is mostly mould and swollen timber, and you'll usually see it coming. Underground leaks concern us more. Water pouring into reactive clay under a slab or footing makes that patch of ground swell while the rest stays dry. Uneven movement like that is how cracks open in brickwork and doors start sticking in their frames. A leak that has run under a slab for a year can leave a repair list well beyond the plumbing.
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