Since November 2024 the maximum delivery temperature at bathroom taps is 50°C, not 55°C — while the cylinder itself still has to sit at 60°C or above. Here is why both numbers matter.
Two numbers govern hot water in a New Zealand house, and they pull in opposite directions: water has to be stored hot enough to kill bacteria, and delivered cool enough not to scald anyone.
60°C in the cylinder
Stored hot water has to sit at 60°C or above. That is a legionella control: the bacteria that cause Legionnaires' disease multiply in warm water and are killed reliably at 60°C. Turning a cylinder down to save power is a genuinely bad idea, and it is a common one.
50°C at the tap
The water arriving at a tap used for personal hygiene — bathroom basin, shower, bath — must not exceed 50°C.
This changed on 1 November 2024. The limit was previously 55°C, and a great deal of plumbing advice online still says 55. The reason for the drop is scald time: at 55°C a child can be badly burned within a few seconds, while at 50°C it takes around 45 seconds. Those extra seconds are usually enough for an adult to react.
How both are true at once
The cylinder stores hot, and a valve cools the water on its way to the bathroom. That device is a tempering valve or thermostatic mixing valve, and one is now required on any new hot water installation or replacement.
Acceptable devices include tempering valves, thermostatic mixing valves, thermostatically controlled taps, and temperature-limited water heaters. Which one suits depends on the system.
The 50°C cap applies to personal hygiene outlets only. The kitchen sink and laundry are treated differently, because dishwashing and cleaning benefit from hotter water.
What this means in practice
Replacing a cylinder? A tempering valve is part of the job now, whether or not the old system had one. On older houses that is occasionally the single biggest surprise in the quote — the valve is cheap, but fitting it sometimes means reworking the pipework around the cylinder.
Water suddenly cooler after a cylinder replacement? That is usually the new valve doing its job. A shower that used to run scalding now tops out lower. If the water is genuinely too cool rather than merely less dangerous, the valve can be checked.
Renting the place out? Scald risk is a real liability question for landlords, and the exemption that lets you do minor plumbing in your own home does not apply to a rental.
Bought a house with an old system? The rules apply at the point work is done, so an existing compliant-when-installed system is not suddenly illegal. But if the cylinder is near the end of its life anyway, the valve comes with the replacement — see when to replace a cylinder.
The one thing not to do
Do not turn the cylinder thermostat down to make the shower safer. It lowers the storage temperature into the range where legionella grows, and it does not reliably fix delivery temperature either. Temperature at the tap is controlled by the valve, not the cylinder.
Tony installs and replaces hot water systems across Paraparaumu, Waikanae, Otaki and the Hutt Valley, tempering valve included as standard. Get a quote or call 021 198 3113.