Legionella guidelines and regulations focus on industrial and commercial systems like cooling towers or health care facilities. Domestic water systems are not in regulations and it’s unlikely they ever will be. However evidence shows that they do pose a risk to susceptible occupants. So what can you do to keep the risk low?

The factors that cause problems with Legionella in domestic systems are the same as in any other system. Correct temperatures, servicing of equipment and keeping water flowing through all your outlets are the three keys to safety. So let’s look at each factor in turn and look at your options!


The Australian Plumbing Code requires that hot water storages (gas or electric) should be kept above 60°C. At this temperature any bugs entering the tank will be killed. It is tempting to turn the water down to save on energy costs. But if you are a susceptible person the results could be disastrous (see left). In this instance turning the water temperature down led to a fatal case of disease from a domestic hot water service.

The SA Health Department advised after this tragic event in 2014 :

“SA Health acting director of public health, Dr Chris Lease, said people should be aware of the risks associated with reducing the temperatures in hot water services – which carry a national requirement to be set at 60 degrees or higher.

“However keeping water at this temperature can increase the risk of scalding injuries, particularly for children and older people,” Dr Lease said.

Dr Lease said anyone unsure of temperature setting should contact their manufacturer or plumber, and said showers or wash basins not used regularly should be flushed with hot water to eliminate any bacteria.”

What about scalding?

Scalding is probably a greater risk than Legionella, particularly for very young and the much less young members of the community. A hot water service can still operate at 60°C to kill bacteria if you fit a device. This device is a ‘tempering valve’ (see left) . It cools the water coming from the heater by mixing with cold water. This still saves on energy bills by reducing the amount of hot water in pipes around the house. It will also reduce the chances of scalding. You can attach tempering valves to both hot water storages and instantaneous heaters. They need installing by licenced plumbers and servicing annually – as does the hot water service.

How Common is the problem?

The statistics on incidence of disease from domestic water systems are a little vague but some data is available. A study in Italy suggests Legionella contamination in more than 1 in 5 water heaters and more with other bacteria (Pseudomonas). Also in Italy, another study found Legionella in both hot water services (30%) and instantaneous heaters (6%). A more recent study in the UK has shown Legionella colonisation in 6% of domestic water systems by traditional test methods and in 30% of domestic water systems using DNA techniques.

What this means in terms of people getting sick is more difficult to work out. What is clear is that outbreaks make up a small percentage of cases each year (typically less than 30%). The rest of the cases are ‘sporadic’ which means ‘at irregular intervals’. In Europe over 30% of cases are sporadic and the source is often a mystery. The inference of this is that domestic water systems are making a significant contribution – but how much is a unknown.

What can I do?

Well there are a few things you can do! Firstly, are you a high risk person? Those with high risks include age (over 50), smoking, existing chest conditions, and a weak immune system (transplant recipient or some arthritis treatments). So if you fit the bill stay calm and take some action.

Always keep the hot water service at 60 degrees or more. If there is a risk of a scald get a tempering valve fitted. There is a picture of one on the left, the valve blue cap of the valve is half way down the heater, to the left of the photo. This valve and the hot water unit need servicing once a year.

If you have taps that don’t get a lot of use (spare bathroom etc) run them for a couple of minutes once a week. Let your shower hoses drain after use to keep water out of them and reduce biofilm. Better still fit a fixed shower head instead!

Make the changes and get peace of mind!

Further Reading

Borella P, et al (2004) Legionella Infection Risk from Domestic Hot Water. Emerging Infectious Diseases 10, 3: 457-464

Martinelli F. et al (2000) A Comparison of Legionella pneumophila Occurrence in Hot Water Tanks and Instantaneous Devices in Domestic, Nosocomial, and Community Environments. Current Microbiology 41, 5:374-6

Collins S. et al (2016) Occurrence of Legionella in UK household showers. International Journal of Hygiene and Environmental Health. In Press.