Signs you have a hidden water leak (and how to check)

Some leaks are obvious, like a dripping tap or a puddle under the sink. Others stay out of sight inside a wall, under a slab or in the pipe that runs under your front yard. Those hidden leaks can waste water for weeks and slowly damage your home before anyone notices.

The good news is that you can usually confirm whether water is escaping somewhere with a few simple checks. This guide covers the warning signs, how to test with your water meter, and when it's time to call a licensed plumber.

Common warning signs of a hidden leak

No single sign proves you have a leak, but a few of these together are worth checking out:

• A water bill that jumps without any change in how your household uses water. Compare it with the same bill from last year, not just the last one.
• A green or soggy patch of lawn that looks different from the grass around it. Sydney Water says this can mean you have an underground pipe leak.
• Damp patches, bubbling paint or swollen skirting boards, especially near the bathroom, kitchen or laundry.
• Musty smells or mould in a cupboard, wardrobe or corner that doesn't get wet.
• Cracked or lifting tiles, or floorboards that feel soft or have started to cup.
• The sound of running water when every tap in the house is off.
• Low water pressure that has crept up on you.

If you notice any of these, run the meter test below.

The water meter test

Your water meter is the simplest way to find out whether water is flowing somewhere it shouldn't. Sydney Water's leak detection page suggests these steps:

1. Turn off all taps and appliances that use water, including drip systems, dishwashers and washing machines.
2. Find your water meter. It's usually at the front of the property. Leave the meter tap turned on.
3. Write down or photograph the numbers on the meter.
4. Don't use any water for at least an hour.
5. Check the numbers again. If they've changed, you have a leak. The bigger the change, the bigger the potential leak.

Some water utilities suggest an overnight test instead. Hunter Water recommends turning off all taps and water-using devices before bed, noting the reading, then checking again in the morning. It notes that the white dials show kilolitres and the red dials show litres, so the red numbers are where a slow leak shows first.

Remember to switch off anything that runs on a timer, such as irrigation, pool top-ups or rainwater tank pumps, or the test will give you a false alarm.

Check the usual suspects first

A moving meter tells you water is going somewhere, but not where. Before assuming the worst, rule out the common culprits that aren't really hidden at all.

Toilets

A cistern that leaks into the bowl can trickle away quietly for months. Water Corporation suggests putting four or five drops of food colouring in the cistern and leaving it for half an hour without flushing. If colour shows up in the bowl, there's a leak. It also lists warning signs such as water around the base of the toilet, staining where water runs down the bowl and a noise that carries on after the flush has finished.

Sydney Water offers another quick check: put a small piece of dry toilet paper at the back of the bowl and make sure it stays dry until the next flush.

Taps, hoses and the hot water system

Sydney Water also suggests:

• checking the expansion valve near the top of your hot water system when you haven't used hot water for a while (it shouldn't leak constantly)
• disconnecting hoses or irrigation pipes that stay connected to garden taps, then checking the taps themselves aren't leaking
• checking taps and toilets regularly for signs or sounds of leaks

If your hot water system is leaking from the tank itself or around the base, that's a job for a plumber. Our guide to hot water system replacement explains what affects the cost if it needs replacing.

When to call a plumber

If the meter keeps moving after you've ruled out toilets, taps and appliances, the leak is probably in a pipe you can't see. Sydney Water notes that for a large leak you'll probably need a plumber with specialist equipment. Leak detection can involve isolating sections of pipe, pressure testing, and listening or thermal imaging tools, so ask the plumber how they plan to find the leak before they start digging or cutting.

While you wait, you can usually turn off the water at the main stop tap near the meter if water is pouring out. Turn it back on only when you need it, and check first whether your hot water system needs to be switched off too.

Who pays to fix it?

As a general rule, the property owner is responsible for the pipes and fittings on their side of the meter. Hunter Water says owners are responsible for maintaining and repairing all pipes and fittings within the property, and that renters should contact their agent or landlord immediately because they may be responsible for usage charges. Arrangements differ between water utilities, so check yours.

Ask about a leak allowance

Some utilities offer help with your bill for a genuinely hidden leak. For example, Hunter Water's Undetected Leak Rebate may give eligible customers an allowance of up to 50% of the increase in water usage, but the fault must be repaired by a licensed plumber and you must apply within 30 days of the bill's due date. Visible leaks, damp walls and faulty taps or cisterns aren't covered. Other utilities have their own rules, so keep your plumber's invoice showing where the leak was and how it was fixed.

Finding a plumber

Plumbing work generally needs a licensed plumber, and rules differ between states. Before you book, check the business's ABN and licence with your state regulator. Our guides on how to choose a plumber and plumbing compliance certificates explain what to look for and what paperwork to ask for.

You can search for plumbers near you on Find My Tradie, or start with plumbers in Sydney and plumbers in Newcastle. Prices vary with the leak, access and the repair needed, so get two or three written quotes for bigger jobs where you can.

Find plumbers in your area

Frequently asked questions

This guide is general information only, not legal or financial advice. Rules change, so check the official sources linked above for your state.