Why there are two temperatures
Stored water has to be hot enough to stop bacteria growing. The Australian Building Codes Board says "Legionella growth is reduced significantly in water stored at 60°C and above", and warns that turning storage down "will promote the growth of legionella". The National Construction Code (NCC) says Legionella control for water heaters "must be carried out in accordance with AS/NZS 3500.4".
Water at that heat can scald, so the code caps what comes out where people wash. Hot water must be delivered at "not more than 50°C" for "all heated water installations for personal hygiene purposes": showers, baths and basins. Kitchens and laundries sit outside that rule.
The three numbers
| Where it applies | Why | |
|---|---|---|
| 60°C or more | Water stored in the heater | Keeps Legionella down |
| 50°C at most | Bathroom fixtures used for personal hygiene. Not kitchens or laundries | Cuts the risk of scalds at home |
| 45°C at most | Residential parts of aged care buildings, patient care areas in health care buildings, areas of early childhood centres and schools used by children, and facilities for people with a disability | Extra scald protection in care and education settings |
The devices that do it
A tempering valve blends hot water with cold so the outlet stays under the limit. For the 50°C limit, the NCC allows a tempering valve or a temperature limited heater. For 45°C, only a thermostatic mixing valve or a thermostatically controlled tap will do.
Don't turn the tank down to stop scalds
Lowering the heater's thermostat swaps one risk for another: water stored below 60°C can let Legionella grow. Scald protection belongs at the outlet, with the right valve. In Queensland, Queensland Health says "Any adjustment to the thermostat settings should be done by a licensed electrician."
Older people and young children
The NCC 2025 adds guidance, not a rule: "if the occupants of a Class 1 building are older adults or young children, a lower temperature than specified in B2D5(b) should be considered." Class 1 covers houses and similar homes. If someone at home is very young or elderly, ask a hot water plumber whether a lower outlet setting makes sense for you.
Replacing a heater: the national rule
Under NCC 2025, a temperature control device is required "When replacing a hot water heater, regardless of the type or location of the heater". The only exemption is where "one or more, but not all water heaters" in a bank are replaced. NCC 2022 worked differently: the rule didn't apply to a replacement in the same location "where the original installation did not require a temperature control valve."
But states vary the code, so the national text isn't the last word. Never assume every replacement needs a valve, or that none does. Here's what we've confirmed.
Tempering valves on replacement, by state
| Needed when you replace a heater? | Bathroom limit | |
|---|---|---|
| NSW | Yes, even like-for-like. Not when only a solar collection panel is replaced | 50°C at "showers, baths, handbasins and bidets" |
| Victoria | Not confirmed. NCC 2022 had a Victorian like-for-like exemption, and NCC 2025 has no Victorian variation. Ask the plumber | 50°C |
| Queensland | Yes, on "all new and replacement hot water systems" | "delivered to taps at a maximum of 50°C" (see below) |
| South Australia | Only if one was fitted before. All solar installations need one, replacements included | 50°C |
| Western Australia | Yes, when a heater is replaced or relocated, except for a basin in a Class 1, 2, 4, 5, 6, 7, 8 or 10 building | 50°C |
| Tasmania | Yes, except a single unit in a bank of heaters | 50°C |
| ACT | Not confirmed. NCC 2025 commenced on 1 May 2026 but isn't mandatory until 1 May 2027 | The national rule applies |
| Northern Territory | Not confirmed | Not confirmed |
Queensland's wording
The Queensland Government's hot water page says water is "delivered to taps at a maximum of 50°C". That's its plain-language summary. The national limit is narrower: it covers fixtures used for personal hygiene, not every tap in the house. Queensland's page also says water "must be heated to a minimum of 60°C to prevent the growth of bacteria such as Legionella".
Signs to get it looked at
- The shower suddenly runs much hotter than it used to.
- Bathrooms run lukewarm while the kitchen tap is hot.
- The temperature swings while you're under the shower.
- Your heater was replaced and nobody mentioned a tempering valve.
- Someone in the house is very young, elderly or has a disability, and you're not sure what the outlet temperature is.
Questions to ask a hot water plumber
- Is there a tempering valve on my system, and is it still working?
- Does my state require one on this replacement?
- What temperature will the bathroom outlets run at?
- Is the storage temperature at least 60°C?
- Would a lower outlet temperature suit our household?
What we would do
Leave the tank at its storage temperature and control scalding at the outlet. If someone at home is very young or elderly, ask about a lower outlet temperature: the national code suggests considering one. When the heater is replaced, ask the plumber what your state requires instead of assuming. A hot water specialist will know your state's rule and can test the valve while they're there.