A Green Valley homeowner rang me last spring with a Sydney Water bill nearly double the one before it. Nothing dripping, no wet patches in the yard, no running toilet. The only odd thing was a strip of kitchen floor that was always a bit warm underfoot. That's a hot water line leaking under the slab, and it had been quietly pouring heated water into the ground for months. A hidden water leak is like that. It doesn't announce itself. It shows up on the bill, and by then it has been running for a full quarter.
Here's the short version. If your water bill is suddenly high and nothing has changed in the house, do the water meter leak test tonight. It costs nothing and takes ten minutes plus an hour of waiting. If the meter moves with everything off, you have a leak on your side of the meter and it's yours to fix. The rest of this post covers the meter test, where Sydney Water's responsibility ends, how water leak detection works, and what it costs. If you want it found today, we are a leak detection plumber, no call-out fee, across South West Sydney.
Turn off every tap and appliance, read the water meter, use no water for at least an hour (overnight is better), then read it again. If the numbers moved, water is leaking somewhere on your side of the meter, and everything past the meter is the property owner's to fix. A plumber finds it by isolating sections and pressure testing, then listening gear, thermal imaging or tracer gas, so nothing gets dug up on a guess.
Why is my water bill so high?
Before you assume the worst, rule out the boring causes. Sydney Water's own figures say a slow dripping tap loses a few litres an hour, while a toilet that runs constantly can waste thousands of litres a day. A toilet is the number one bill wrecker I see, and it's often silent: a worn flush valve washer lets water trickle from the cistern into the bowl without a sound. Put a few drops of food colouring in the cistern, wait 15 minutes without flushing, and if colour shows up in the bowl you've found it. The running toilet post covers the fix, and the flexi hose post covers the other quiet one under the vanity.
| What you notice | Likely cause | What to do |
|---|---|---|
| Bill up, nothing visible, meter moves overnight | Concealed leak in a wall, under the slab or in the underground service line | Isolate and test, then leak detection |
| Warm patch on the floor, hot water runs out faster | Hot water pipe leaking under the slab | Turn off the cold inlet to the hot water system and re-test the meter |
| Green strip of lawn in a dry yard, soft or sunken ground | Underground water service or irrigation line | Re-test the meter with the irrigation isolated |
| Faint hiss at a tap or cistern when the house is quiet | Toilet inlet valve, flush valve or a tap washer | Food colouring test, then a washer or valve replacement |
| Puddle at the hot water system | Pressure relief valve or tank failure | A small drip while heating is normal; a steady stream needs a plumber |
| Damp cupboard under the sink or vanity | Flexi hose or trap | Turn off the mini stop tap and replace the hose |
The water meter leak test, step by step
This is the same test Sydney Water tells customers to do, and it's the first thing I do on a leak job. Your meter is usually at the front of the property near the boundary, sometimes in a small pit with a lid.
- Turn off every tap inside and out, and make sure the washing machine, dishwasher, irrigation, evaporative cooler and any pool auto-fill are off.
- Read the meter and write the numbers down. On most Sydney Water meters the black digits are kilolitres (thousands of litres) and the red digits are litres.
- Use no water for at least an hour. Overnight is better, because a small leak might only tick over a few litres in an hour.
- Read it again. If the red digits have moved, water has gone somewhere while everything was off. That's a leak.
Some meters also have a small dial or spinning star that turns with even a tiny flow. If that's moving while everything is off, same answer. A note on hot water: the meter measures cold water coming into the property, so a hot water leak still shows, because the tank refills as it loses water.
Narrowing it down before you ring anyone
If you have a tap at the meter and a separate stop tap at the house, you can do a second test. Turn the water off at the house stop tap and watch the meter. If it still moves, the leak is in the underground service line between the meter and the house. If it stops, the leak is inside the house or in the hot water system. Turn off the cold inlet to the hot water system and test again. If the meter stops then, you've narrowed it to the hot water side, which is exactly what that Green Valley slab leak turned out to be.
Whose pipe is it: yours or Sydney Water's?
Sydney Water owns the meter and the water main, and it will generally repair the service between the main and the meter, up to about one metre inside your boundary, at no charge. Everything downstream of the meter, the pipes and fittings running to your house and taps, is the property owner's to repair. If the leak is at the meter itself, or the ground is wet on the street side of it, ring Sydney Water on 13 20 90 first. If it's on your side, that's where I come in. Sydney Water's leak detection page sets this out.
How water leak detection actually works
The old way was to dig where the ground was wettest and hope. Water travels a long way along pipe bedding and under slabs, so the wet spot is often nowhere near the leak. A water leak detection plumber works by elimination, then confirmation. I isolate sections of the system and put a pressure gauge on each one: hot versus cold, the underground service versus the house, downstairs versus upstairs. The section that won't hold pressure is the one with the problem. Then I pin it down with acoustic listening gear (a ground microphone picks up the hiss of water escaping under pressure), thermal imaging for hot water lines under tiles, and tracer gas for the stubborn ones, where a harmless gas is pushed through the drained pipe and a detector finds where it surfaces. For drains and stormwater, the CCTV camera does the looking instead.
The point of all that gear is a small hole in the right place instead of a trench across the wrong one. For a leak under the slab there are usually two options: open the floor at the exact spot and repair the pipe, or abandon that section and run a new line around it, through the ceiling or along an external wall. The second one is often cheaper and cleaner, especially in a finished kitchen. For a failed underground service line under a driveway, I can bore a new one with the Grundomat from a small launch pit and leave the concrete alone.
Leak detection in Sydney: what it costs
The detection itself is quoted on inspection, because the time depends on how many sections need isolating and whether a wall or floor has to be opened to confirm. What moves the price is access, the number of possible lines, and whether it's after hours. On the repair side, Sydney 2026 price guides put a burst pipe repair at $230 to $920, a leaking tap repair at $92 to $300, call-out fees at $69 to $170 and hourly rates at $92 to $230, most around $140. You get a price from me before the work starts.
One thing worth knowing: Sydney Water offers a hidden leak allowance. If a licensed plumber finds and repairs a concealed leak, you can apply for a credit, which for residential customers is 50 per cent of the water usage charge for the worst affected quarter, once per property every five years. Keep my invoice. You'll need it for the application.
When to call a plumber
If water is running out of somewhere and you can't stop it, turn it off at the meter and ring the emergency line. There's a separate post on what to do in the first ten minutes with a burst pipe. If the meter is moving but nothing is flooding, you can safely leave it until business hours, especially if you've narrowed it to hot or cold with the tests above. Just don't sit on it for another quarter. Landlords in Fairfield should also know that a leaking tap or toilet can cost you the right to charge tenants for water usage, which is covered on our water efficiency certificates page. Done right. Done once.
Monarch Civil & Plumbing finds and fixes hidden leaks across South West Sydney and the Macarthur region. See our leaks and burst pipes page, find your plumber in Green Valley or plumber in Fairfield, or ring 0455 222 292. Emergencies are 24/7; everything else gets a same-day reply.
Related guides: water meter leak test and burst flexi hose.
Need it sorted? Ring 0455 222 292 any hour or book online. Monarch Civil & Plumbing is a leak detection plumber, no call-out fee, quoted on inspection, same rate day or night.
Emergency in Liverpool or Campbelltown right now?
Ring 0455 222 292 and Paul answers. emergency plumber Liverpool and emergency plumber Campbelltown say what to shut off while he is on the way; everywhere else within about 20 km of Austral the 24/7 emergency plumber page covers it. Same rate day or night, no call-out fee.
Frequently asked
How do I know if I have a hidden water leak?
Do the water meter leak test. Turn off every tap and appliance, read the meter, use no water for at least an hour, then read it again. If the numbers have moved, water is escaping somewhere. Other signs are a bill that jumps with no change in how you live, a warm patch on the floor, a green strip of lawn in a dry yard, damp skirting boards or a faint hiss when the house is quiet.
Who is responsible for a water leak before the meter?
Sydney Water owns the meter and the main, and it generally repairs the service between the main and the meter, up to about a metre inside your boundary, at no charge. Ring Sydney Water on 13 20 90 if the meter itself is leaking or the ground is wet on the street side. Everything after the meter, including the underground service to the house, is the property owner's to repair.
How does a plumber find a leak under a concrete slab?
By elimination first, then confirmation. I isolate the hot and cold lines and pressure test each one to find which won't hold. Then thermal imaging shows a hot water leak through the tiles, and acoustic listening or tracer gas pinpoints a cold one. Once it's located you can open the floor at that exact spot, or, often cheaper, abandon that section and run a new line through the ceiling or along a wall.
Does Sydney Water give a rebate for a hidden water leak?
Yes. It's called the hidden leak allowance. If a licensed plumber finds and repairs a concealed leak, you can apply for a credit on your bill. For residential customers it is 50 per cent of the water usage charge for the most affected quarter, and each property can claim once every five years. Keep the plumber's invoice, because you will need to show the leak was found and fixed by a licensed tradesperson.
Why is my water bill so high when I can't find a leak?
Start with the meter test, because a leak you cannot see is still a leak the meter can. If the meter is dead still with everything off, look at usage instead: a running toilet that only leaks after a flush, irrigation timers, a pool auto-fill, a new tenant or a teenager discovering long showers. Also compare the reading on the bill with the meter itself, since an estimated read can be corrected.
How much does leak detection cost in Sydney?
The detection is quoted on inspection, because the time depends on how many sections have to be isolated and whether a wall or floor needs opening to confirm the spot. Access and after-hours work move the price. For the repair, Sydney 2026 price guides put a burst pipe repair at $230 to $920 and call-out fees at $69 to $170. I give you the price before the work starts, and the hidden leak allowance can claw some of it back.
Licensed plumber and drainer based in Austral, 13+ years in the trade, working across Liverpool, Fairfield and the Macarthur region. About Paul