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How to Find a Water Leak in Your House: A Plumber's Diagnostic Guide
How to Find a Water Leak in Your House: A Plumber's Diagnostic Guide, a Prime Plumbing & Gasfitting plain-English guide to how to find a water leak in your house for Melbourne homeowners. Below we cover what works, what doesn't, and when to call a licensed plumber.
Quick answer: Find a hidden water leak by (1) reading your water meter with everything off, if it still ticks, you have a leak somewhere; (2) isolate sections by closing isolation valves and re-checking the meter; (3) check the obvious places first (under sinks, behind toilet, hot water unit, under the dishwasher, irrigation); (4) check for damp patches on walls, ceilings or floors; (5) listen for hissing or running water in walls. If the meter ticks but you can't find the source visually, it's likely concealed (in a wall cavity, under floor, or in the slab) and needs a plumber with leak detection equipment.
If your water bill has jumped, a wall feels damp, or you can hear water running when nothing's on, you might have a leak. Here's the diagnostic process we use on a callout, same one you can run yourself before deciding to book.
Step 1: The water meter test (do this first)
The single most diagnostic test for a hidden leak. Five minutes.
- Turn off everything that uses water in the house: taps, dishwasher, washing machine, toilets, irrigation, hot water unit (if it's gas, leave the gas on but make sure it's not actively heating)
- Find your water meter: usually at the front of the property, in a small in-ground box near the boundary
- Note the position of the dials, including the small leak indicator (a small star, triangle or circle that spins on the slightest flow)
- Wait 15-30 minutes without using any water
- Re-read the meter
If the dials moved or the leak indicator is spinning → you have a leak somewhere on the property.
If nothing moved → no leak (or the leak is very intermittent, might be worth retrying later if you suspect one).
This test is the gold standard. A plumber will do this first thing on a leak callout.
Step 2: Isolate sections to narrow down the leak
If the meter test confirmed a leak, the next step is figuring out roughly where. Most properties have a few isolation points, close them in sequence and re-read the meter to localise the leak:
- Close the toilet isolation valve (at the base of the toilet, behind it). Re-read meter for 5 min. If meter stops, leak is at the toilet (cistern fill valve, flush valve, or pan connector).
- Close the hot water unit isolation valve (next to the unit, on the cold supply). Re-read meter. If meter stops, leak is somewhere on the hot water side or in the unit itself.
- Close the irrigation isolation valve (if you have garden irrigation). Re-read meter. If meter stops, leak is in the irrigation system.
- Close internal isolation valves to bathroom/laundry/kitchen if your house has them. Re-read meter after each close. The room where the meter stops is the leak location.
If you can stop the leak by isolating a specific section, you've narrowed it from "somewhere on the property" to "somewhere in this room", much easier for a plumber to repair.
Step 3: Check the obvious places first
Before calling a plumber, walk the property and look for:
Under sinks (kitchen, bathroom, laundry)
Look in the cabinets, water staining on the cabinet base, drips at the P-trap, weep at the isolation tap connection. Most accessible leaks. Take a torch.
Behind and around toilets
Check the floor behind the toilet for damp. Lift the cistern lid and listen for hissing (suggests a faulty fill valve continuously dripping into the bowl). Add a few drops of food colouring to the cistern, wait 15 minutes, if colour appears in the bowl without flushing, you've got a flush valve leak (silent water waste).
Hot water unit
Look around the base of the tank for water staining. Check the pressure-relief valve discharge pipe, should drip a tiny amount during heat-up cycles only, never constantly. Continuous dripping suggests over-pressure or a faulty valve. See hot water replacement for end-of-life unit signs.
Dishwasher and washing machine
Check behind/under each appliance. Inlet hoses develop weeps over time. Check the floor in the cabinet next to the dishwasher.
Outdoor taps and irrigation
Walk the garden, soft patches in lawn, areas that are unusually green or brown for the weather, dripping outdoor taps, drip-irrigation lines that are over-watering one spot.
Visible damp patches on walls or ceilings
Tap the wall, sounds different where there's moisture inside. Look for water stains, paint bubbling, mould near skirting. Ceiling stains directly below a bathroom usually mean a shower or bath waste leak.
Step 4: Listen
Walk through the house with everything off and listen. Specifically:
- Hissing in walls = pressurised supply line leak
- Slight running water sound in walls = same
- Drip-drip above a ceiling = waste pipe leak
- Gurgle in drains = drain partial blockage, not necessarily a leak
A leak large enough to make sound is also large enough to be losing measurable water. Confirm with the meter test.
When to call us
Book a leak detection visit if:
- The meter test confirms a leak but you can't find it
- You see damp patches you can't explain
- Water bill has jumped without a usage change
- You hear water running when nothing's on
- A previous leak repair didn't actually solve it
We diagnose using acoustic + thermal equipment, locate the leak precisely, and quote the repair separately so you know the full cost before approving.
Service area
Prime Plumbing & Gasfitting services water leak detection across Melbourne's eastern, south-eastern, inner-east and bayside suburbs. See all suburbs we service →
Book a leak detection
Suspected leak you can't find? Call 0475 407 670 or send your address + a description of the symptom through the contact form.
- BPC #103414: Building and Plumbing Commission licence
- Type A gasfitting endorsement for gas appliance work, held on the BPC licence
- 4.8 stars on Google
- Fixed-price written quote before any work
- Compliance Certificate issued where the work requires one
Related: Water Leak Detection Melbourne · Burst Pipe Repair Melbourne
About the author
Alister Williams is the founder and lead plumber of Prime Plumbing & Gasfitting. He's been licensed under BPC #103414 for over a decade, holds Type A Gasfitter endorsement with Energy Safe Victoria, and is a member of the Master Plumbers Association of Victoria.
Step 5: When you can't find it: call a plumber with leak detection equipment
If the meter test confirms a leak but you can't find the source after the obvious-places walk, the leak is concealed: in a wall cavity, under floor, or in the slab. At that point you need professional leak detection:
- Acoustic leak detection: listening equipment that picks up the hiss of pressurised water escaping inside walls or under slabs
- Thermal imaging: pressurised hot/cold supply lines show on infrared even when the visible surface looks normal
- Tracer gas: for slab leaks, an inert gas pumped into the supply line emerges through the slab where the leak is, picked up by a sniffer
- Borescope: small camera fed through small access holes to inspect wall cavities
Our water leak detection page covers this in detail. We carry acoustic and thermal equipment as standard on leak callouts.
What about water bills creeping up but no visible damp?
This pattern is almost always one of three things:
- Toilet flush valve dripping silently into the bowl: the cistern keeps refilling. Easy to test (food colouring trick above).
- Slab leak under the floor: water disappears into ground, no visible damp because it's leaking into soil. Common on older Melbourne properties with copper supply lines run through the slab.
- Outdoor irrigation leak: drip lines develop micro-leaks; or a buried supply line to a tap or garden bed has corroded.
The meter test plus isolation testing will localise which.
When to Call a Licensed Plumber
Some plumbing problems are DIY-friendly; others need a licensed professional under Victorian law.
Anything involving gas, sewer drainage, hot water units, backflow prevention, or work behind tiled walls must be handled by a licensed plumber or gasfitter.
Frequently asked questions
The leak indicator on most domestic meters spins at flows as low as 1-2 millilitres per minute, that's roughly a slow drip per second. So if the indicator isn't spinning, you don't have a measurable leak. If it's spinning slowly, even a tiny drip counts.
Yes. A persistent leak that doesn't show as visible damp is usually one of: flush valve drip into toilet bowl (silent), slab leak (water escapes into ground), or supply line in a wall cavity (water tracks down inside the wall before showing). All three need to be found and fixed, and the longer they run, the more damage they cause.
Usually yes, acoustic and thermal equipment locates leaks through finished surfaces. Once located, a small access hole is typically enough to repair. Modern leak detection has dramatically reduced the "let's open the wall to see" approach.
Generally home insurance covers water damage caused by a leak (carpet, floors, ceiling) but the plumbing repair itself is classed as maintenance. Some policies cover hidden water leak detection costs separately. Check your specific policy wording.
Minimum 15 minutes with everything off. For very slow leaks, you can leave the meter for an hour and compare readings. The longer the test, the smaller a leak it'll catch.
This is a more advanced version of the meter test. Read the meter at bedtime, turn off the main valve, leave for 8 hours, re-read in the morning. If readings match, you have no leak between meter and house. This eliminates an in-house leak from a meter-side leak (rare but possible).
Toilet flush valve drip, usually under $100 in parts and a 30-minute visit. It's also one of the most common leaks. Worth checking first.
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?
If you're unsure, Prime Plumbing & Gasfitting can inspect the issue and explain the options before any work starts. Call 0475 407 670 or request a quote online.
