How to manage your water systems to prevent Legionella

Cathal Walsh
Environmental Journalist
Friday, 12th July 2019
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How to manage your water systems to prevent Legionella

Legionnaire’s disease is a potentially fatal type of pneumonia which can be contracted through inhaling water droplets. Such droplets can be created, for example, by: hot and cold water outlets; atomisers; wet air conditioning plant; and whirlpool or hydrotherapy baths. Every household and premises has fixtures capable of spreading legionella droplets so it is worth everyone’s while to be vigilant of it.

Luckily you can manage and monitor the water systems in your home to minimise the risk of the bacteria spreading. Here are a few tips on how to do that


Temperature control

Legionella bacteria multiply between 20-45 degrees Celsius. They are dormant below 20 degrees and they do not survive above 60 degrees. Utilising this information you can manage your water fixture controls to minimise legionella growth.

  • Water storage cylinders should store water at 60 degrees Celsius or higher
  • Hot water should be distributed from its fixtures at 50 degrees or higher ideally, or as hot as possible without incurring a risk of scalding
  • Cold water should be distributed from fixtures at temperatures below 20 degrees.


It is importantly to routinely check, inspect and clean your water system. You should check the temperature of the sentinel outlets of your water cylinder monthly. The sentinel outlets of a tank are the furthest and closest outlets to the tank. You should also check the temperature of your hot water tank every month and any cold water storage tank every six months.

Water system design

Legionella growth is most rampant in stagnant waters. To reduce risk you should try and remove any dead ends in your pipe work which may allow stagnant water to pool. Flush out infrequently used fixtures at least weekly. You should also clean and descale hoses and showerheads at least quarterly and clean out your water tanks frequently.

You can design your system to prevent legionella growth by :

  • keeping pipe work as short and direct as possible;
  • adequately insulating pipes and tanks;
  • using materials that do not encourage the growth of Legionella;
  • Preventing contamination, eg by fitting tanks with lids and insect screens.                                                                                                                             

Water analysis

You should take a sample of your water and get it tested for legionella regularly to ensure that the bacteria in your system is at an acceptable level.


Other methods of preventing legionella include copper and silver ionisation and biocide treatments, however these should not be used instead of a proper maintenance system, rather in conjunction with it.

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