What Temperature Should Hot Water Be?

Hot water in Queensland has two target temperatures, and they do opposite jobs. Water stored in a home hot water tank must be heated to at least 60°C, which is hot enough to stop bacteria such as Legionella growing. Water delivered to the bathroom (the shower, the bath and the basin) should arrive at no more than 50°C, which the Queensland Government describes as enough for washing while cutting the risk of a scald.

The gap between those two numbers is closed by a temperature control device, such as a tempering valve, that blends cold water into the hot supply before it reaches the bathroom. So a tank sitting at 60°C or more and a shower that tops out around 50°C is not a fault. It is a hot water system working the way it was designed to.

If a bathroom tap runs much hotter than that, or the tank never gets properly hot, one half of the arrangement is not doing its job, and the rest of this guide explains which half and what to do about it.

Stored hot water is kept at 60°C or above to control Legionella, the bacteria behind Legionnaires' disease. Queensland Health says hot water systems, including shower roses, taps, tanks and pipework, can harbour Legionella where water is stagnant or warm, in the range of 25 to 50°C. A tank held at 60°C keeps the stored water out of that range.

That is why Queensland Health's advice runs against a common instinct. It says not to turn hot water systems down and not to switch them off unnecessarily, and that the booster on a solar system should stay on during cloudy days rather than letting the tank drift into the warm range.

Two habits from the same advice are worth adopting at home. After a long time away, let the system heat water to 60°C for at least half an hour before anyone uses it. And each week, run any hot or mixed shower or tap that has not been used at full flow for at least 15 seconds, keeping your face out of the spray so you do not breathe it in.

Bathroom hot water is capped because water hot enough to control bacteria is hot enough to cause a serious burn almost at once. A Queensland Government plumbing guideline puts it plainly: water delivered at 60°C takes one second to cause third-degree burns, while water delivered at 45°C takes six hours.

The same guideline notes that the risk is far greater for children, older people and people with a disability, who may react more slowly and have thinner skin. Kidsafe Australia makes the same point about young children, saying hot water from the tap at 60°C can burn a young child in less than a second. It recommends limiting bathroom and ensuite hot water to a maximum of 50°C, with a licensed plumber installing the mixing valve.

So the 50°C limit is not a comfort setting. It is a ceiling that gives a child, or anyone slow to pull away, time to react before the skin is damaged.

Queensland requires a temperature control device whenever a hot water system is installed or replaced, including a straight like-for-like swap. That last part catches people out. The national plumbing code applies the rule to new installations, and a Queensland guideline made under the Plumbing and Drainage Act 2018 states that in Queensland, new includes like-for-like replacements of existing hot water systems.

Under that guideline, a device is required when a water heater is installed for the first time, replaced with the same type or a different type, or relocated and reconnected to the bathroom fixtures it served. It is also required when more than one bathroom fixture is replaced, as in most bathroom renovations, and when the hot water service is extended to new fixtures such as a new ensuite, in which case only the new fixtures need it.

A device is not required when a single fixture or its tapware is replaced, when only solar collector panels are replaced, or when a valve, element or thermostat is replaced. Even then, the guideline recommends considering one. The table on this page sets out each case.

The 50°C limit applies only to fixtures used mainly for personal hygiene: showers, baths and hand basins. The Queensland guideline says the requirement does not apply to other fixtures such as a kitchen or laundry tap, so fitting a temperature control device to those is optional.

Depending on how a house is plumbed, that can mean the kitchen tap runs hotter than the shower, and that is allowed. If young children live in the house, keep it in mind when filling a sink or a bucket from the kitchen or laundry, because the bathroom limit does not protect those outlets.

If you would rather have the kitchen limited too, it is a reasonable thing to raise with a plumber when the system is next replaced or serviced. It is a choice for the household, not a requirement of the code.

Yes, 45°C is fine for washing, and in some buildings it is the required maximum. Under the Plumbing Code of Australia provisions quoted in the Queensland guideline, bathroom fixtures must deliver no more than 45°C in the residential parts of aged care buildings, in patient care areas of health care buildings, and in parts of early childhood centres and schools used by children. The bathrooms of ordinary houses and units fall under the 50°C ceiling that applies in all other cases.

Those settings also need a more precise device. Where the 45°C limit applies, only a thermostatic mixing valve or a thermostatically controlled tap is accepted. For the 50°C cases, a tempering valve or a temperature limited water heater is accepted as well.

Queensland Health's Legionella advice puts washing and bathing water at 45 to 50°C, so a household can choose the lower end, for example where a young child or an older relative lives there. A plumber sets that at the temperature control device, not by turning the tank down.

Every type of hot water system has to meet the same bathroom limit, but they get there in different ways. For a home, the code accepts four kinds of temperature control device: a tempering valve, a thermostatic mixing valve, a thermostatically controlled tap, or a temperature limited water heater.

A storage tank, whether electric, gas, solar or heat pump, holds its water at 60°C or more, so the bathroom supply has to be blended down with cold water before it reaches the outlet. A tempering valve is a temperature activated mixing valve that does this, and it is accepted for a house. A thermostatic mixing valve uses a thermostatic element or sensor to hold the mixed water at a preselected temperature, and it is one of the two devices accepted where the 45°C limit applies.

A continuous flow system heats water as it passes and stores none. Queensland Health lists thermostats that can be regulated for instantaneous water heaters as one form of temperature controller. Whether a particular continuous flow unit meets the limit on its own depends on the model and the installation, so ask the installer rather than assuming. In every case the delivery temperature has to be achieved in line with AS/NZS 3500.4.

If the shower is too hot, the safe fix is at the temperature control device, not the tank. Turning a storage tank below 60°C works against the Legionella control the setting exists for, and Queensland Health's advice is plain: do not turn hot water systems down. It adds that any adjustment to thermostat settings should be done by a licensed electrician.

Adjusting or replacing a tempering valve is plumbing work. The Queensland Building and Construction Commission (QBCC) says most plumbing work in Queensland is regulated and must be done by a QBCC licensed plumber or drainer, and that even minor work, such as maintaining, repairing or replacing a fitting, must be done by a licensee. The QBCC's examples of unregulated work, which anyone may do without a licence, are small jobs such as replacing a shower head or a tap washer. Tempering valves and water heaters are not among them.

So the owner's part is to notice and report. Leave the valve and the thermostat cover alone, note what is happening, and book a licensed plumber to check the system. Any change to a thermostat setting is, in Queensland Health's words, a job for a licensed electrician.

A few signs suggest a system is no longer holding the right temperatures. A bathroom tap is noticeably hotter than it used to be. The shower never gets properly warm while the kitchen tap is hot, which can suggest the temperature control device, since the kitchen tap does not have to sit behind that device. The water is lukewarm at every tap, including the kitchen, which suggests the water is not being heated properly rather than a temperature limit at work. Or the system has been off or unused for a long stretch and nobody knows whether it has been back up to 60°C.

None of these calls for opening anything. Write down which taps are affected and when it started, and pass that to a plumber. If you manage a rental, a tenant reporting a scalding or tepid shower is worth acting on promptly, because a missing temperature limit and a tank running too cool both carry a health risk.

Kidsafe's bath time advice holds whatever the system: turn the cold tap on first and off last, and check the bath water before a child gets in.