Rising energy prices have many of us looking for new ideas to save energy and reduce bills. One of these ideas is to turn down your storage hot water heater. However, this could also be a health hazard.

One of the many energy saving tips currently doing the rounds is to reduce the storage temperature of your water heater. The idea being that the water only needs to be around the same temperature as the human body (about 37°C) and this will reduce costs by not heating the water to a level higher than you need when you are using it.

However, if you have a storage water heater, there is actually a very good reason why the water inside is kept at a much higher temperature than you need; that reason is to avoid the growth of a number of potentially dangerous pathogens, most notable of which is the Legionella bacteria.

Legionella is a common waterborne organism that grows in water at temperatures between 20°C and 45°C. It can cause illnesses such as Legionnaires’ disease, which is a pneumonia that causes lung inflammation. It can affect anyone, but age, illness, immunosuppression or other risk factors, such as smoking, greatly increase susceptibility.

Legionella growth is reduced significantly in water stored at 60°C and above, which is why the storage water heater will keep your water at such a high temperature.

What all this means is that if you turn the storage temperature down to around 37°C, there is a very good chance that it will promote the growth of legionella which could make you sick.

There are other ways to reduce the cost of heated water, such as switching to off-peak power for water heating, or upgrading to a more efficient system. A licensed plumber can also provide appropriate, professional advice on how to reduce energy costs for your existing heated water system.

Important note

This article is about the storage temperature of heated water, which is the temperature it is kept at inside the tank.

It does not apply to delivery temperature, which is how hot the water is when it comes out of the tap. There are separate limits for delivery temperature to reduce the risk of scalding from taps in showers, bathrooms, etc.

These rules are in Part B2 of NCC Volume Three. If you are unsure, talk to a licensed plumber or your state/territory plumbing regulator for detailed advice on how to avoid legionella growth and reduce the risk of scalding.