What is Legionella and why do I need regular assessments?

Your frequently asked questions – answered

What is Legionella?

Legionella is a naturally occurring bacteria. When the bacteria enter water systems in the manmade environment, conditions can often encourage accelerated growth and reproduction to levels which can cause bacterial pneumonia and be fatal to humans. Therefore, legionella is considered a biological hazard and is listed under the COSHH Regulations and you will need a risk assessment to cover water systems in the work place.

How do you get Legionnaires’ disease?

Legionnaires’ disease is contracted by inhaling small water droplets which can be suspended in the air known as aerosols and will create a risk to susceptible individuals. The infection is clearly linked to susceptibility.  Highly susceptible individuals may get infected even at relatively low doses. The HSE deem a domestic water system to be under control if legionella is maintained below 100cfu/l.

In environments where there are particularly susceptible individuals, like in the NHS there needs to be controls in place at all times.

How is Legionnaires’ disease treated?

Legionnaires’ disease is treated with antibiotics but without treatment it can be fatal. Many antibiotics are highly effective against Legionella bacteria.

What are the symptoms?

The symptoms are very similar to that of flu and therefore can often be overlooked:

  • High temperature, feverishness and chills
  • Cough
  • Sputum
  • Muscle pains
  • Headache
  • Pneumonia
  • Diarrhoea
  • Signs of mental confusion

Do I need a risk assessment?

A legionella risk assessment is required to cover water systems in any commercial premise. This includes rented housing particularly where communal services are present.

How often should you update the Legionella risk assessment?

Legionella risk assessments should be updated regularly (every two years at least) or when significant changes occur that may render the current risk assessment invalid.

How often should you review a risk assessment?

A legionella risk assessment should be updated at least every two years.

But if you’ve had changes to the water systems the risk assessment will need to be updated. We would always recommend an annual review to ensure the systems are being suitably managed.


Do all work places need a Legionella risk assessment?

Where water is used or stored which can be transmitted in an aerosol and then be inhaled, there will be a reasonably foreseeable risk of exposure to legionella bacteria.

Therefore, if you have water on your site, you will need to carry out a legionella risk assessment to identify the level of risk.

Ask yourself, does the Health and Safety at work Act Apply to your situation? If the answer is yes, then you most definitely need a legionella risk assessment, even in a brand new building!

What happens after the Legionella risk assessment?

If the legionella risk assessment is low or negligible risk, you may not need to do anything else apart from review the risk assessment every two years.

If there is a risk of legionella infection then a control scheme will be required to manage the risks. However, for a basic domestic system the control scheme need not be complicated.


How can you control Legionella?

Prevention is better than cure, so we wanted to share with you some measures that can be adopted to create water systems that are hostile to the growth of legionella. Traditionally, temperature is used to control legionella and should wherever possible be the first act of defence.

Temperature control

Cold Water – Cold water should be stored below 20°C and distributed to all outlets within two minutes of opening the tap below 20°C then the cold water circuit will not encourage bacterial growth including legionella growth.

Hot Water – Hot water should be stored at 60°C and distributed and supplied to all outlets above 50°C within 1 minute of operation.

StagnationStagnation can be prevented by introducing routine flushing programmes and reducing the volumes of stored water.


If you want to find out more about the Legionella risk assessments that we can provide, or other related services click here.


Why not find out a bit more about the services we have to offer or if you’d like to join our team, we’d love to hear from you!
As always, if you need a fast and quality response to your reactive repairs, get in touch today. We have our helpline open 24/7 so we’re always available when you need us.

National Maintenance
National Maintenance

You currently have JavaScript disabled!

This site requires JavaScript to be enabled. Some functions of the site may not be usable or the site may not look correct until you enable JavaScript. You can enable JavaScript by following this tutorial. Once JavaScript is enabled, this message will be removed.