Legionella bacterium are commonly found in building domestic hot water plumbing and are a potential source of infections that can cause deadly pneumonias (Legionnaires’ disease) and other illnesses. Proper management of domestic hot water systems, and regular monitoring, is essential to control the growth and spread of this dangerous pathogen. 

The genus Legionella is made up of more than 50 waterborne species, primarily associated with fresh and natural water systems such as rivers, lakes, streams and wetlands. Of these, only a very small number have been found to be pathogenic. The most common species known to cause infection is Legionella pneumophila. 


About Legionella in domestic hot water

Legionella has an optimal multiplication temperature of between 25-45 degrees Celsius and can survive and multiply in domestic hot water systems that are maintained at or below that temperature. If left unchecked, the bacteria can potentially infect individuals by inhalation. To prevent such an infectious outbreak, building owners and managers need to be aware of the risks associated with Legionella and how it can be managed and controlled.

About Legionella in domestic hot water

The most effective strategy to combat Legionella is to prevent its growth in the first place. This can be done by implementing secondary water disinfection such as copper silver ionization and ensuring that all hot water systems are adequately maintained and monitored. Hot water tanks and other associated equipment should be regularly inspected for leaks or any signs of corrosion, scale or sediment. In addition, water should be maintained at the right temperature, ideally between 55-60 degrees Celsius. This is the temperature at which Legionella will not thrive, but where other bacteria can still live and multiply. However, these temperatures can be logistically challenging to maintain at distal points of use and why secondary disinfection should be continually implemented.

In addition to maintenance and temperature control, regular testing should also be conducted to ensure Legionella is not present within the potable water distribution network. This can involve carrying out tests on water samples taken from outlets and hot water systems. If the results come back positive, then it will be necessary to treat the water however this should not be the case for when secondary water treatment has been implemented. Some short term treatments involve chlorination, depending on the type and concentration of Legionella, yet the outcome is normally short lived and will require a more permanent secondary water treatment solution such as copper silver ionization.

Finally, building owners and managers should also consider maintaining a logbook or database of any work done to the hot water system, such as inspections, maintenance, and testing. This will help to identify any issues or warning signs relating to Legionella, as well as allowing a quick response if an outbreak were to occur. 

In conclusion, Legionella is a dangerous bacterium that can cause deadly infections and illnesses. Building owners and managers need to be mindful of this risk and take proactive action to prevent its growth or spread in the hot water system. This includes regular monitoring, maintenance, disinfection and testing. By conducting these steps, they can help ensure the safety of their staff and visitors, as well as helping to contain any potential outbreaks before they can cause serious harm.


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