28 July 2017

Legionella prevention in hot water systems

Hot water systems provide the ideal conditions for legionella bacteria to multiply (bacteria are most active between 20C-45C.)

Hot water systems provide the ideal conditions for legionella bacteria to multiply (bacteria are most active between 20°C-45°C.) Hot water tanks and pipes are also prime areas for water stagnation, corrosion and the build-up of scale deposits which act as a source of nutrients for bacteria to grow.

If you are responsible for the maintenance of a hot water system, you should eliminate the risk of hosting a thriving legionella bacteria source. This is particularly important in establishments that are most vulnerable, including:

  • Schools
  • Hospitals
  • Care facilities
  • Restaurants
  • Hotels

What steps should you take to prevent legionella?

The procedures below will help to keep your hot water systems safe.


Risk Assessment

Risk Assessment

It is important to perform a risk assessment of your hot water system to obtain a clear indication of possible threats. This will enable you to prepare for any controls needed to prevent a legionella outbreak.



On site testing and analysis is a necessary precaution in order to spot the signs of legionella before it becomes a problem. Identifying issues in time will save a lengthy and costly process to remove legionella from the premises.

Temperature control

Temperature control

Water in hot water systems should be stored at 60C or higher as legionella bacteria cannot survive at this range. There is a scald risk if water is dispersed at 60C so considerations should be made to install thermostatic mixer valves to mix the stored water with cold water before it is distributed.

Pre-treatment equipment

Using the right pre-treatment and application equipment helps to safe-guard against the risks of legionella growth by keeping water clean and free from scale deposits.

Boiler treatment


Hot water treatments are the most effective preventative maintenance measures for hot water systems. They protect your boiler system from the build-up of corrosion, limescale and carryover and help to keep water clean and bacteria-free.

Taking measures to prevent legionella reduces the risk of outbreaks of legionnaires disease, which can cause serious illness and in some cases, death.

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