Prevent scalding from tap water

Lowering the hot water delivery temperature

The maximum allowable hot water delivery temperature for new personal hygiene fixtures has been reduced from 55°C to 50°C, for most buildings. 

Hot water in residential housing is required to be no hotter than 50°C when it comes out of the tap at personal hygiene fixtures, such as hand basins, baths, showers and bidets.

It’s important to note that the maximum hot water delivery temperature reduction is not retrospective. That is, it only applies to the temperature of hot water delivered to new sanitary fixtures used for personal hygiene installed on or after 2 November 2024, when using the acceptable solutions as a means of compliance. 

For institutions with persons that are at greatest risk from scalding, such as schools, hospitals and care homes, the maximum hot water delivery temperature for personal hygiene fixtures remains 45°C.

For early childhood education and care centres, the Ministry of Education requires the temperature of water delivered from taps that are accessible to children does not exceed 40°C.

Minimising scalding risk 

Children often receive serious scalds because they have more sensitive skin than adults and burn more quickly.

Elderly people can be vulnerable due to sensitive skin, disabilities or slow reaction times.

For example:

• a child is left in a bath with the hot tap running, while the parent or caregiver is distracted by their cell phone 
• a child turns on the hot tap, falls into the bath, and can’t get out
• an elderly person falls and injures themselves when showering, accidentally adjusting the water to the hottest setting and unable to get out of the hot shower water.

The table below shows the type of scalding burn injury based on time of exposure to various water temperatures. (Dansk Standard, 2009).

(e) = estimate.

This table indicates that at a temperature of 55 °C, the time it takes for a child to get a full thickness scald burn is 8 seconds. At 55°C, it takes less than four seconds for a child to get a 2nd-degree burn.

When the temperature of water is reduced to 50°C, the time it takes for a child to get scalded increases to 45 seconds. For adults the time it takes to get a full thickness scald burn increases from about 30 seconds to around 5 minutes.

Below 50°C the likelihood of scalding continues to decrease. 

Note: Maximum hot water delivery temperatures are not bathing temperatures. You should still mix cold water with hot water for baths and showers. 

You can reduce the risk of scalding by:

• installing a hot water delivery temperature control device
• always running cold water first
• never leaving a child alone in the bathroom

Delivery temperature control 

Hot water delivery temperature control devices play a critical role in preventing scalding by ensuring that water delivered to hand basins, baths, showers and bidets stays within a safe temperature.

Acceptable hot water delivery temperature control devices include thermostatic mixing valves (TMVs), thermostatically controlled taps, tempering valves (TVs), and temperature limited water heaters (TLWH). These devices must only be installed or adjusted by a licenced plumber.

Thermostatic Mixing Valves (TMVs) 

TMVs blend hot and cold water to a pre-set temperature. They react quickly to changes in water temperature and pressure to maintain a consistent output temperature. If there is a failure in the cold water supply, TMVs automatically shut off the hot water flow, preventing dangerously high water temperatures from being delivered to taps. 

TMVs are commonly provided in institutions with persons that are at greatest risk from scalding, such as such as schools, hospitals and care homes. 

TMVs are an acceptable temperature control device where a maximum delivery temperature of 45°C is required.

Thermostatically Controlled Taps 

Thermostatically controlled taps function similarly to TMVs by blending hot and cold water to a safe, pre-set temperature directly at the tap. 

Thermostatically controlled taps are an acceptable temperature control device where a maximum delivery temperature of 45°C is required.

Tempering Valves (TVs)

TV’s work similarly to TMVs by mixing hot and cold water but are simpler in design. TVs are commonly installed downstream of a storage water heater to reduce the hot water temperature before it is delivered to taps or showers.

TVs are an acceptable temperature control device where a maximum delivery temperature of 50°C is required.

Instantaneous Temperature Limited Water Heaters (TLWH)

An instantaneous (continuous flow) TLWH is a water heater that limits the delivered hot water temperature at the outlet of any fixture supplied by the water heater, without the need for an additional temperature control device.

TLWHs that meet AS 3498 are an acceptable temperature control device where a maximum delivery temperature of 50°C is required.

Evaluating alternatives

Delivery temperature control devices that are not manufactured in accordance with standards cited in Acceptable Solution G12/AS1 may be considered by a building consent authority as an alternative solution. 

The guidance provided below includes factors for consideration when assessing if alternative delivery temperature control devices supplying heated water to basins, baths, showers or bidets will comply with the Building Code. Information on some of the items below may be able to be obtained from the manufacturer or supplier of these products.

When evaluating the alternative delivery temperature control devices, factors to consider include determining if they incorporate equivalent safety features to those prescribed in the delivery temperature control device standards cited in G12/AS1.

Factors to consider may include: 

• Suppled factory adjusted to not deliver/produce water above 50°C. 
• Not readily adjustable by end users to deliver/produce water above 50°C. 
• Provide a steady state delivery temperature once installed and commissioned, including during hot water flow variation conditions. 
• Operate safely or fail safe. 
• Include clear and detailed instructions on how to install and commission the device.

Mitigating legionella risks

Water that’s too hot creates the risk of scalding. But water that’s not hot enough creates the risk of harmful legionella bacteria growing in storage water heaters.

The solution to this problem is to store hot water at a minimum temperature of 60°C, and deliver it to baths, showers, basins and bidets at a temperature no greater than 50°C. Installing a delivery temperature control device is one way of achieving this.

In hot water flow and return circulating systems, the water returning to a water heater, or a hot water storage vessel, must not be less than 55°C, to control the growth of legionella. This applies to systems complying with the design and installation requirements for hot water circulating systems in AS/NZS 3500.4, which is cited in G12/AS3 (Note: hot water circulating systems are outside the scope of G12/AS1). In these systems, hot water delivered temperature control devices must be provided at, or near to, personal hygiene fixtures.

When hot water delivery temperatures apply

Maximum hot water delivery temperatures apply to new plumbing fixtures used for personal hygiene, such as hand basins, baths, showers and bidets. However, they do not apply to kitchen sinks and laundry tubs, as these are not considered sanitary fixtures used for primarily for personal hygiene. 

While higher temperature hot water can be provided to kitchens and laundries, the provision of 50°C hot water to these fixtures and appliances in residential housing is optional. The provision of 50°C hot water to domestic kitchen sinks is usually adequate for hand-washing dishes. 

To avoid contractual issues and complaints, designers and plumbers should discuss the configuration of the hot water piping system and what best serves the clients purposes prior to the installation.

Note: Untempered hot water must not be provided to fixtures or appliances from a storage water heater that is connected to an uncontrolled heat source, such as a wet-back or solar water heater.

For existing buildings, maximum hot water delivery temperature provisions apply to the installation of new sanitary fixtures for personal hygiene. However, this requirement is not extended to existing fixtures or appliances within a building. 

Hot water systems installed before 1992 are unlikely to have temperature control devices fitted. Speak to a licensed plumber about installing a temperature control device.

How to comply with Building Code requirements

You can comply with the prevention of scalding provisions of Building Code clause G12 Water Supplies by following the provisions set out in:

Acceptable Solution G12/AS1 section 6.14 Safe water temperatures.

All guidance related to G12 Water supplies