Maintaining the correct water temperature in your home is about far more than just personal comfort during a morning shower. In New Zealand, the way we heat, store, and use water is a matter of public safety and legislation.

If you own a home or manage a property, understanding the intersection of the NZ Building Code and your plumbing system is important. The Building Code comes under the umbrella of the Building Act 2004, and is enforced by the Ministry of Business, Innovation and Employment (MBIE). This NZ government legislation is there to ensure you have the water in your home at the correct temperature.
In this guide, we explore the legal requirements for hot water in NZ, the health risks associated with incorrect settings, and the practical steps you can take to ensure your system is efficient and compliant.

Navigating The NZ Building Code And Legislation

The regulations surrounding hot water temperatures are found within the New Zealand Building Code. This document acts as a performance-based set of rules that all buildings must meet. Unlike some international codes that dictate exactly how a pipe must be laid, the NZ Building Code focuses on how the building must perform for its inhabitants. Specifically, the plumbing and drainage sections ensure that water systems provide a safe environment.

The Ministry of Business, Innovation and Employment oversees these standards under the Building Act 2004. This means that these rules are not merely suggestions from your plumber; they are mandatory legal requirements. The primary goal of this legislation is to prevent two distinct but equally dangerous outcomes: the growth of harmful bacteria and the occurrence of life-changing scald injuries.

What Is The Ideal Temperature Of Your Hot Water?

The most important rule in the New Zealand plumbing standard involves the storage of water. If you have a traditional hot water cylinder, the water inside must be kept at a minimum of 60 degrees Celsius. This specific temperature is not chosen at random. It is the thermal threshold required to eliminate the risk of Legionella bacteria.

Legionella thrives in warm, stagnant water, typically between 20 and 45 degrees Celsius. If your cylinder is set too low to save on power, it becomes a breeding ground for these organisms. When you turn on a shower, the bacteria can be inhaled through the mist or fine spray. This leads to Legionnaires’ disease, which is a severe and potentially fatal form of pneumonia. Symptoms often include high fever, cough, and shortness of breath. By keeping your storage tank at 60 degrees, you ensure that any bacteria present are neutralised before they ever reach your bathroom.

What About Temperature At The Tap?

This is a great question! While water must be stored at 60 degrees, it should never reach your skin at that temperature. The Building Code dictates that for residential homes, the maximum delivery temperature at the tap is 50 degrees Celsius. This reduction is achieved through the use of a tempering valve.

The 10-degree difference between storage and delivery is a crucial safety buffer. Human skin, particularly that of a child or an elderly person, cannot withstand 60-degree water for more than a few seconds without sustaining a third-degree burn. At 50 degrees, the risk of a deep tissue scald is significantly reduced, giving a person time to react and move away from the stream of water.

In specific high-risk environments, the delivery requirements are even stricter. For buildings like early childhood education centres, hospitals, and nursing homes, the limit is capped at 40 degrees Celsius. This is because the occupants of these buildings may have thinner skin or slower reaction times, necessitating an even higher level of protection against heat.

How Quickly Can Hot Water Burn The Skin?

To appreciate why these regulations are so strict, we have to look at how quickly heat transfers to human skin. A common misconception is that hot water only causes minor redness. However, at the temperatures found in many unregulated cylinders, the damage is instantaneous.

If your water is at 68 degrees, it takes only one second to cause a third-degree burn. At 60 degrees, the same level of damage occurs in five seconds. By the time a toddler realises the water is too hot and tries to pull their hand away, the damage may already be permanent. This is why the 50-degree delivery limit is so critical for our homes.

Furthermore, water that is consistently too hot can have long-term effects on skin health. It strips away natural oils, which can lead to chronic dryness, itching, and the worsening of conditions like eczema. For those with high blood pressure or heart conditions, the shock of extremely hot water can also place unnecessary strain on the cardiovascular system.

Financial Impacts And Energy Efficiency

Setting your hot water temperature correctly is also a matter of financial responsibility. Water heating typically accounts for about 30 percent of the average New Zealand household energy bill. If your thermostat is set significantly higher than 60 degrees, you are essentially paying to overheat water that you will eventually just mix with cold water at the tap anyway.

By maintaining the 60-degree storage and 50-degree delivery standard, you maximise the efficiency of your cylinder. You are keeping the water hot enough to be safe, but not so hot that your heating element is running constantly. Additionally, you can save money by ensuring your pipes are well-insulated. This prevents heat loss as the water travels from the cylinder to your bathroom, meaning your system does not have to work as hard to maintain the required delivery temperature.

How Do You Control The Temperature Of Your Water?

Modern plumbing offers several ways to manage these temperatures effectively. If your home is older, you may need to upgrade your components to meet current standards.

• Tempering Valves: The tempering valve is the hero of residential plumbing. It is a three-way valve that takes the 60-degree water from your tank and mixes it with cold water before it enters your home’s internal plumbing. This ensures that no matter how hot the tank is, the water at the tap stays at a safe 50 degrees.
• Cylinder Thermostats: Every hot water cylinder has a thermostat, usually located behind a small panel. While it is possible to adjust this yourself, it is often best left to a professional to ensure it is calibrated correctly. It must be high enough to kill bacteria but not so high that it damages the cylinder or the pipes.
• Thermostatic Mixing Valves: These are often used in commercial settings or for specific fixtures like a high-end bath to regulate the temperature of the water before it comes out of the tap. They provide very precise control over the temperature and can be adjusted to specific degrees for maximum comfort and safety.
• Instantaneous Or Continuous Flow Water Heaters: Unlike cylinders, these systems heat water on demand. Most modern units come with digital controllers that allow you to set the output temperature to exactly 50 degrees. This removes the need for a tempering valve in many cases and ensures you never run out of hot water.

Maintaining Your System For The Long Term

To ensure your system remains compliant and safe, it is wise to have a professional plumber perform a check-up every few years. Over time, tempering valves can become clogged with mineral deposits, and thermostats can lose their accuracy. A quick check of the temperature at the kitchen sink and the bathroom shower can tell you if your system is still performing as it should.

If you have recently moved into an older home, it is particularly important to check these settings. Older installations may not have tempering valves, meaning the water at your tap could be a dangerous 60 degrees or higher.

Homeowner Compliance And Safety Checklist

1. Test The Temperature At The Tap: The most direct way to check compliance is to measure the water temperature. Using a basic kitchen thermometer, run your bathroom tap for about 30 seconds until the temperature stabilises. For most New Zealand homes, this should not exceed 50 degrees Celsius. If your water is reaching 55 or 60 degrees at the tap, your system is likely non-compliant and poses a significant scalding risk.
2. Locate Your Tempering Valve: Look at the pipes coming out of your hot water cylinder. You should see a brass valve where the hot pipe and the cold pipe meet before heading into the wall. This is your tempering valve. If you cannot find one, your system might be older and could be sending boiling water directly to your showers. Installing one is a vital safety upgrade and is now mandatory for any new or replacement cylinder installations under the 2024 Building Code updates.
3. Check The Cylinder Thermostat: While the tap should be 50 degrees, the tank itself must be hot. Check the thermostat on your cylinder. It should be set to 60 degrees Celsius. This is the legal minimum required to kill Legionella bacteria. If it is set lower to save power, you are at risk of bacterial growth. If it is set much higher, such as 70 or 80 degrees, you are wasting a significant amount of money on your energy bill.
4. Inspect The Pressure Relief Valve: There is a safety valve on your cylinder, often with a small lever, designed to release pressure so the tank does not burst. Check the drain pipe connected to this valve. It usually leads to the outside of your house or up through the roof. If you see constant dripping or steam coming from this pipe, your valve might be failing, or your temperature might be set too high, causing the system to bleed energy and water.
5. Look For Signs Of Valve Failure: If you have a tempering valve but your water temperature fluctuates wildly between hot and cold during a shower, the valve may be failing. Mineral deposits can build up inside these valves over time, causing them to stick. Other signs of a failing valve include reduced water pressure or water that stays lukewarm even when the cylinder is fully heated.
6. Visual Inspection For Corrosion: Take a close look at the base of your cylinder and the pipe joints. Any signs of green oxidation on copper pipes or rust on the tank jacket are red flags. In New Zealand, a hot water cylinder is expected to last around 10-15 years. If yours is older and showing signs of wear, it may be time to discuss a modern, more efficient replacement with a professional.

Proper water temperature management is a simple step that leads to a safer, more efficient, and more comfortable home environment. Need help with your water temperature or hot water cylinder? Call the professionals at Whitehead Plumbing & Gas today!

Please note: The information provided in this post is for educational purposes only and is not a substitute for professional plumbing advice. Setting your water heater temperature involves risks, including potential scalding if set too high or the growth of Legionella bacteria if set too low. Always consult your water heater’s manufacturer’s manual and local building codes before making adjustments. If you are unsure of how to safely calibrate your unit, please contact a licensed professional plumber to prevent injury or property damage.