PERTHHot water scald control: 50 degrees, and why it's stored hotter
WA requires heated water delivered at max 50C to showers, baths and basins. The 1 May 2024 expansion, the Legionella balance, tempering valves
The hot water coming out of your bathroom tap is not allowed to be as hot as the water sitting in your hot water tank, and the reason is scald prevention. Western Australia's rules on heated water delivery temperature tightened in 2024, and while it is a plumber's obligation, it is worth a homeowner and a buyer understanding, because it involves a valve that wears out on a schedule.
The rule
Heated water delivered to the outlets of fixtures used primarily for personal hygiene, showers, baths, basins and bidets, has a maximum allowable delivery temperature, set to protect against scalding. Building and Energy set this out in Industry Bulletin 149, and Industry Bulletin 161 reminded the industry of the requirements that applied from 1 May 2024, when WA's plumbing regulations moved to reference the current Plumbing Code of Australia.
The requirement applies to all heated water installations, including when a water heater is replaced, relocated or added to an existing system. So a simple hot water unit swap can bring the obligation into play on an older home that never had it.
Why the tank runs hotter than the tap
Here is the tension the rule manages. The water in the storage tank has to be kept hot, hot enough to kill Legionella bacteria, which multiply in warm water. But water that hot at the tap will scald a child or an older person in seconds. The solution is to store hot and deliver cooler: the tank stays at a safe-from-bacteria temperature, and the water is tempered down before it reaches the hygiene fixtures.
That tempering is done by a valve, a tempering valve or a thermostatic mixing valve — that blends hot and cold to hold the delivery temperature at the safe maximum. It is a real device, plumbed in near the water heater, and it is doing safety-critical work every time someone turns on a tap.
The part that matters to an owner
These valves do not last forever. Under the relevant standard, tempering valves are largely non-serviceable and require replacement at intervals not exceeding five years. A valve past its life can drift, and a drifting valve on the scald side is a genuine hazard, particularly in a house with young children or elderly occupants.
So on an older home the practical question is not just whether a tempering valve is fitted, but how old it is. A valve installed with a hot water system a decade ago and never touched is well past the replacement interval, whatever it is currently delivering.
Where it fits an inspection
The operation and adequacy of plumbing and hot water systems is specialist work, and AS 4349.1 places the detailed testing of these outside a building inspection's scope — it is a licensed plumber's job. What a pre-purchase inspection can do is note the hot water system, its apparent age, and visible signs around it, and flag where a plumber's attention is warranted — and an ageing or absent tempering valve is exactly that kind of flag.
If you are buying an older Perth home, particularly for a family, it is a small, cheap item to have a licensed plumber confirm, and a genuine safety one. It sits alongside the other transfer-time safety checks — smoke alarms and RCDs — that are easy to sort before settlement and awkward after.
How a scald actually happens
The reason the delivered hot water temperature is regulated comes down to how quickly hot water injures skin, and the numbers are more alarming than most people expect. The margin is small. Water hot enough to cause a serious scald does so in seconds, and the thinner, more delicate skin of young children and the elderly burns faster and at lower temperatures than an adult's. A tap left running hot, a child who turns the wrong tap, an elderly person slow to react, these are the ordinary domestic moments that a temperature limit at the tap is designed to make survivable rather than catastrophic. The requirement to deliver hot water to bathroom fixtures at a controlled temperature is not bureaucratic caution; it is a direct response to how scald injuries happen and who they happen to.
This is why the requirement targets the fixtures used for personal washing in particular. It is at the basin, the bath, and the shower that a person, and especially a vulnerable person, is in direct and sustained contact with the water, and it is there that an uncontrolled hot temperature does its damage. The kitchen and laundry, where hotter water is useful and the contact is different, are treated differently. The regulation is precise about where the limit applies because it is precise about where the risk is.
Why the tank is hot but the tap should not be
There is an apparent contradiction that confuses people: the hot water system is deliberately kept hot, hotter than the safe delivery temperature, and yet the water at the bathroom tap has to arrive cooler. Both are true and both are necessary. The storage tank is kept hot to control Legionella, the bacteria that can grow in warm water and cause serious illness; storing water below a certain temperature invites that risk, so the tank runs hot on purpose. But water at that storage temperature is too hot to deliver safely to a washing fixture, so it has to be brought down before it reaches the tap.
The device that reconciles these two requirements is the tempering valve, which blends the hot stored water with cold to deliver it at a controlled, safe temperature to the bathroom fixtures. It is a small, inexpensive component doing an important job: satisfying the anti-Legionella requirement and the anti-scald requirement at once. When it is present and working, the system is both safe from bacteria and safe from scalding. When it is missing, or has failed, the water arriving at the tap can be at or near the storage temperature, which is scalding, and that is precisely the fault the requirement exists to prevent.
What this means at inspection and for an owner
For a building inspection, hot water temperature is one of the checkable safety and compliance items, and it is one where a simple observation can flag a real hazard. Where the delivered temperature at a bathroom fixture is clearly too high, that points to a missing or failed tempering valve, and it is reported as a defect with a safety dimension rather than buried in general observations, because a scald risk in a house with children or elderly occupants is exactly the kind of finding a buyer needs stated plainly. It is also, usefully, one of the cheaper defects to remedy: fitting or replacing a tempering valve is straightforward plumbing work, not a major expense.
For an owner, particularly one with young children or elderly family members, it is worth knowing that this protection exists and can fail silently, because a tempering valve that has degraded over time can let the delivered temperature creep up without anyone noticing until someone is hurt. It fails silently. It is one of the quiet safety systems in a house that is easy to take for granted, and confirming that it is present and working, on an inspection before purchase or as ordinary maintenance, is a small thing that prevents a serious one.
Common questions
What temperature should hot water be delivered at in WA?
No hotter than 50 degrees Celsius at showers, baths and basins, the fixtures used primarily for personal hygiene. Kitchen and laundry outlets are not subject to this delivery limit.
Why is hot water stored hotter than 50 degrees?
To kill Legionella bacteria, which breed in water stored below about 60 degrees. The water is stored hot and tempered down to a safe delivery temperature by an approved valve near the fixtures.
Does replacing a hot water system trigger the scald rule?
Yes. From 1 May 2024 the delivery-temperature control applies to all heated water installations when the heater is replaced, relocated or added, not just new builds.
This comes up on every pre-purchase building inspection and pre-settlement inspection we carry out.
Read next: wet areas are the most commonly failed part of a new build and ventilation, condensation and mould: the moisture a house can't get rid of.
Sources
Read rather than recalled. Summarised here; the documents themselves are Crown copyright and are linked rather than reproduced.