Plumbing, hot water and hidden leaks: what to check
Hidden leaks are the costliest plumbing problem, and the cheapest check is the water meter: turn every tap off, note the reading, and check again later. An unexplained rise in your water bill points the same way. Look under sinks and vanities, at flexible tap hoses and around the hot water system. Hot water should be stored at 60°C or more to control Legionella and delivered at no more than 50°C to bathrooms; in Victoria, systems installed before 5 August 1998 are unlikely to be tempered. Older galvanised steel pipes can corrode inside, and plumbing work must be done by a licensed plumber.
- 01LeaksTaps off, read the meter, wait, read it again
- 02StoredAt least 60°C, to control Legionella
- 03DeliveredNo more than 50°C to bathrooms
A rising bill with a dry house usually means a hidden leak.
Finding hidden leaks
Many expensive water problems start as a slow leak nobody sees: under a vanity, inside a wall, under a slab or in the garden. QBCC's maintenance guide suggests watching for an unexplained increase in your water bill, checking under sinks and around taps, and inspecting flexible hoses, which can fail and flood a home.
| Check | How | What a fault looks like |
|---|---|---|
| Water meter test | Turn off every tap and appliance, read the meter, wait an hour without using water, read it again | The reading has moved, or the meter’s leak indicator is turning |
| Water bills | Compare usage with the same period last year | An unexplained jump |
| Under sinks and vanities | Look and feel for damp, swelling and staining | Damp cupboard floors, swollen panels, drips at connections |
| Flexible tap hoses | Check the braided hoses under sinks and basins | Rust, fraying, kinks or bulges; replace before they burst |
| Toilets | Listen for running water; add food colouring to the cistern | Colour appears in the bowl without flushing |
| Outside | Walk the garden and the base of walls | Persistent wet patches, lush growth or sinking in dry weather; see site drainage |
A leak near the house can also wet the soil under footings, which matters for reactive clay and termites. Read it with the cracks and termites guides.
What the pipes tell you
| Material | Where you find it | What to know |
|---|---|---|
| Galvanised steel | Older homes, often pre-war and early post-war | Corrodes from the inside, reducing flow and causing leaks and discoloured water |
| Copper | Very common from the mid-twentieth century onward | Durable, but joints can leak and pinhole corrosion occurs in some water conditions |
| Plastic (PEX and similar) | Newer homes and repairs | Flexible; check fittings and that it is protected from sunlight |
Low pressure at some taps, rust-coloured water when a tap first runs, or many patched joints suggest ageing pipework. A licensed plumber can tell you whether to repair sections or replace runs. Sewer and stormwater pipes are a separate system; older clay sewer pipes can be cracked or blocked by tree roots, which a CCTV drain camera can confirm.
Hot water: temperatures and the system itself
Victoria's Building and Plumbing Commission (formerly the Victorian Building Authority) explains the two temperatures that matter. Hot water must be stored above 60°C to prevent Legionella bacteria growing, and delivered at no more than 50°C to showers, baths and basins in homes, because water at 60°C can scald in about a second. A tempering valve blends cold water in to bring the delivered temperature down. In Victoria, systems installed before 5 August 1998 are unlikely to be tempered.
| Check | What to look for |
|---|---|
| Age and type | The compliance plate shows the manufacture date; storage, continuous flow, heat pump or solar |
| Leaks and rust | Water around the base, rust streaks or a damp floor |
| Relief valve and drain | The pressure and temperature relief valve and overflow drain discharge safely, not against the house footings |
| Tempering valve | Whether one is fitted for bathrooms, especially on older systems |
| Gas systems | Flue condition and clearances; servicing by a licensed gasfitter |
Many manufacturers recommend operating the relief valve lever periodically, and servicing the system to their schedule. Check the manufacturer’s instructions for your unit, and leave adjustment and repairs to a licensed plumber.
What to ask before you buy
A standard building inspection does not test plumbing. Ask the age of the hot water system, whether there have been leaks or insurance claims, and for plumbing compliance certificates for any bathroom or kitchen renovation. If the home is older or has large trees near the sewer line, consider a drain camera inspection. For the bathroom itself, see the waterproofing guide.
Common misreads
| What people say | What is closer to right |
|---|---|
| "No visible water, so no leak" | Leaks inside walls, under slabs or in the garden often show only on the meter or the bill. |
| "Turning the hot water down saves money safely" | Storage below 60°C risks Legionella. Lower the delivered temperature with a tempering valve instead. |
| "The relief valve dripping means it is broken" | Some discharge can be normal operation; constant flow or none at all needs a plumber’s check. |
| "Old pipes are fine if the water runs" | Galvanised pipes can be heavily corroded inside while still flowing. |
Worked example: a rising bill and a dry house
Illustrative reasoning example, not an inspected property. A household’s water bill has risen by a third with no change in use. There are no visible leaks inside.
A meter test with every tap off shows the reading moving. Shutting off the supply to the house at the main tap stops the meter, so the leak is inside the house rather than on the garden line. A plumber pressure-tests the system and finds a failing joint under the slab near the laundry. The repair is defined and the insurer can be told early, with the meter readings and bills as evidence.
Frequently asked questions
How do I check for a hidden water leak?
Turn off every tap and water-using appliance, read the water meter, wait an hour without using water, and read it again. If it has moved, there is likely a leak. An unexplained rise in your water bill is another sign.
What temperature should hot water be in Australia?
Stored at 60°C or more to prevent Legionella, and delivered at no more than 50°C to showers, baths and basins in homes. A tempering valve blends in cold water to lower the delivered temperature.
Do older hot water systems have tempering valves?
Often not. In Victoria, systems installed before 5 August 1998 are unlikely to be tempered. A licensed plumber can fit a tempering valve or thermostatic mixing valve.
Should flexible tap hoses be replaced?
Inspect them regularly and replace any with rust, fraying, kinks or bulges. Failed flexible hoses are a common cause of sudden flooding.
What are the problems with galvanised water pipes?
Galvanised steel pipes, common in older homes, corrode from the inside, reducing water pressure and causing leaks and discoloured water.
Does a building inspection check plumbing?
No. A standard pre-purchase inspection does not test plumbing services. Use a licensed plumber, and consider a drain camera inspection for older sewer lines.
How this guide was researched
We start with the cheapest diagnostic, the water meter, then read pipe materials, hot water temperatures and system checks, and separate owner observation from licensed plumbing work.
Limits: The 5 August 1998 tempering date is Victorian; other states differ. All plumbing and gas work must be done by licensed practitioners.
Sources
- Hot water safetyBuilding and Plumbing Commission (formerly the Victorian Building Authority) · accessed
- Your essential home maintenance guideQueensland Building and Construction Commission · accessed
- AS 4349.1-2007 Inspection of buildings, Part 1: Pre-purchase inspections, residential buildingsStandards Australia · accessed
- AS/NZS 3500.4:2025 Plumbing and drainage, Part 4: Heated water servicesStandards Australia · accessed