There’s water on the floor under the tank, and you’re not sure how long it’s been there. If your hot water system is leaking, the first few minutes matter most. You don’t need to diagnose anything yet. You need to stop more water going in and make the unit safe. Then you can work out where the leak is coming from.
The short answer
If your hot water system is leaking, do these three things in order:
- Close the cold water tap on the pipe that feeds into the tank.
- Switch off the power or gas to the unit.
- Find where the water is coming from before anyone uses hot water again.
If water is pouring out and you can’t stop it, call an emergency plumber in Sydney.
Move 1: shut the water into the tank
Most storage hot water systems have a tap on the cold water pipe that feeds into the tank. It’s usually close to the unit, often low on one side.
- Turn it clockwise to close it.
- Turn it gently. If it’s stiff or won’t move, don’t force it.
- No tap, or it won’t close? Turn off the water to the whole property at the meter tap instead.
Closing the cold supply stops the tank refilling, which slows the leak down. If you’ve had to turn the water off at the meter, our guide on what to do when a pipe bursts covers the same shut-off steps.
Move 2: switch off the power or gas safely
With the water off, make the unit safe.
- Electric systems: switch off the hot water circuit at your switchboard. It’s often labelled “HWS” or “hot water”. Keep your hands dry, and don’t touch the switchboard if you’re standing in water.
- Gas systems: turn the gas control on the unit to off, following the instructions on the unit’s label.
Don’t try to drain the tank yourself. Leave that to a licensed plumber, who can do it safely.
Move 3: find where it’s actually leaking
Once the water and power are off, have a careful look. Where the water is coming from tells you a lot.
- From the top: look at the pipe connections and fittings where water goes in and out.
- From the relief valve: the valve near the top of the tank, usually with a small pipe running down from it.
- From the base of the tank: water pooling under the tank, with no obvious source higher up.
Take photos of each area. They’ll help your plumber understand what’s happening before they arrive.
The relief valve
The relief valve is a safety device. It’s designed to release water if the pressure or temperature inside the tank gets too high.
If water is coming from the relief valve, don’t block it, tie it off or try to stop it. A licensed plumber can check whether the valve is doing its job, or whether it’s faulty or the system has another problem. A steady stream from the valve is a sign to book a repair, not to wait and see.
Repair or replace?
Whether your hot water system can be repaired depends on where the leak is.
- Fittings, connections and valves can often be repaired or replaced on their own.
- Leaks from the tank itself are harder to fix, and may mean the tank needs replacing.
Your plumber will confirm which applies once they’ve inspected it. If you need a new system, our hot water repairs team can talk through the options. If your gas system has failed, our guide on whether to replace it with gas or switch to electric may help you decide.
Before the plumber arrives
A few details make the first visit quicker and help your plumber bring the right parts:
- The type of system: electric, gas or another type. The label on the unit usually says.
- The brand and model: also on the label. Take a clear photo of it.
- Where the water is coming from: the top fittings, the relief valve or the base of the tank.
- When you first noticed it, and whether it has got worse since.
- What you’ve already done: for example, closed the cold water tap and switched off the power or gas.
- Whether you rent or own, so your plumber knows who to send the report and invoice to.
In the meantime, keep children and pets away from the area, and mop up any standing water once the power is off.
Renting? Here’s what to know
If you rent in NSW, a broken hot water service is classed as an urgent repair. As at October 2026, the NSW Government’s list of urgent repairs includes:
- a failure or breakdown of any essential service for hot water
- an appliance, fitting or fixture that uses water, or is used to supply water, that is broken or not working properly, so that a substantial amount of water is being wasted
- a burst water service
The NSW Government says tenants must tell the landlord or agent about urgent repairs straight away. If they don’t fix it, check your tenancy agreement for the approved repairers and follow the NSW steps for getting urgent repairs done. It’s a good idea to keep a written record of when and how you reported it.
For help, contact NSW Fair Trading on 13 32 20. This is general information, not legal advice.
FAQs
What do I do if my hot water system is leaking?
Close the cold water tap into the tank, switch off the power or gas to the unit, then find where the water is coming from. If you can’t stop the water, call an emergency plumber.
Can I still shower if my hot water system is leaking?
It’s best to wait. Once you’ve closed the cold water supply, the tank won’t refill, and using it could make things worse. Have a licensed plumber check the system first.
Why is my hot water system leaking from the bottom?
Water under the tank can come from a fitting or valve higher up, or from the tank itself. Check the fittings and the relief valve first. If there’s no source higher up, have a plumber inspect the tank.
How do I turn off the water to my hot water system?
Find the tap on the cold water pipe feeding the tank and turn it clockwise. If there’s no tap, or it won’t close, turn off the water at the meter tap.
How long will a hot water system last once it starts leaking?
There’s no way to say. A leaking system won’t fix itself, so it’s worth having a plumber check it as soon as you can.
Tips
- Show every adult in the house where the cold water tap and the hot water switch are.
- If a slow drip is coming from a fitting, put a container under it, but still book the repair.
- Take photos of the leak before your plumber arrives.
- If you rent, report the problem to your agent or landlord straight away, and keep a written record.
Water under the tank right now?
If water is still coming out, or you can’t make the system safe, call our emergency plumber in Sydney. We cover homes and businesses across Sydney, including Western Sydney. For anything else, visit Sigma Plumbing, your local plumber in Sydney.
