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Legionnaires Disease: Legionella Bacteria in Hot Water Tanks

Many people don’t realise that hot water tanks can be a breeding ground for the bacteria that causes Legionnaires Disease. 

Legionnaires Disease is a very serious condition, being a potentially fatal illness.

The good news is that it is totally preventable.

You need to be informed to protect your family’s health…

What is Legionnaires Disease & How to Prevent it?

Legionnaires’ Disease from Your Hot Water Tank

Legionnaires Disease, or Legionellosis, is a illness caused by a bacteria, Legionella pneumophila.

♦ It is a respiratory disease that can cause severe pneumonia and it is sometimes fatal.

♦ Keeping the hot water tank set to a minimum of 60°C prevents bacteria growth.

♦ Turning your hot water tank down, to save money, can backfire if you go below 60°C

♦ Plumbers know to set the temperature correctly

♦ The best advice is to leave it as set by your plumber

Legionnaires Disease Hot Water Heater

The Legionella bacteria can multiply exceptionally well in warm water, between 25° to 50°C.  
If infected water is inhaled in small airborne droplets of the water, as would happen when taking a shower, the individual could end up with the disease.
The solution is to keep the hot water INSIDE the tank set to a minimum of 60°C. 

Electric storage hot water tank

This applies to all electric and gas storage tank systems, including solar and heat pump units, which also have storage tanks. 
Your plumber would have set your system up to run at 60°C when it was installed. 
Tempering or mixing valves are used to reduce the temperature to prevent possible scalding.  These mix cold water with the hot water AFTER it leaves your tank. 
Your plumber will typically set the tempering valve to deliver 50°C water at the hot water tap. 
Most tankless hot water systems are factory pre-set to 50°C, so they do not require the use of tempering valves.

Added Hazard with Electric Storage Tank Hot Water Heaters

The World Health Organisation -- WHO -- recommends that water be heated and stored at 60°C. 

However, Canadian studies have shown, even when the thermostat is set at 60°C, a high percentage -- approximately 40% -- of electric water heaters remain contaminated because of the lower temperature, about 30°C to 40°C at the bottom of the tank.

No water heaters using gas were contaminated. 

The authors concluded that, because of design variables, use of an electric water heater was the most significant factor leading to Legionella contamination in hot water in the home.

How can this still go wrong? 

Some homeowners unknowingly reduce the temperature setting on their hot water system to conserve energy.  
A good idea in theory, but a bad idea in view of the Legionella issue.  
Some homeowners shut off their hot water tanks when they go on holiday, but an outdoor hot water tank in the sun may provide the perfect conditions for the bacteria to multiply. 
Old or malfunctioning hot water heaters may also have actual temperatures below 60°C, potentially causing the problem. 
Regular inspections by a licensed plumber can help ensure that the problem is prevented.

Tankless Continuous Flow Systems Solve The Problem

Another solution is the use of continuous flow hot water heaters.  
These systems are tankless, so there is no breeding ground for the bacteria. 
They heat the fresh incoming water as it passes through the unit. 
As they only need to heat the water to 50°C and only run when you need hot water, they save energy and money, too. 
Another advantage of continuous flow systems is that they never run out of hot water. 



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The information in this article is derived from various sources and is believed to be correct at the time of publication. However, the information may not be error free and may not be applicable in all circumstances.