June 29, 2023

Practical steps on how to manage legionella risk in your building.

The first step towards ensuring your property is safe from Legionnaire’s disease is to identify and assess the risk of Legionella.
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What is legionella?

What is legionella?

Legionella is a pathogenic bacterium responsible for heath conditions collectively referred to as legionellosis, including the serious, potentially fatal flu-like condition Legionnaires’ disease.

The bacteria occur naturally in aquatic environments including rivers, lakes and ponds, usually at low concentrations, but has also been found in soil and potting composts.

It becomes problematic when it enters engineered water systems where under the right conditions, it can grow to dangerous levels if left untreated.

The disease caused by Legionella bacteria is Legionnaires’ disease and can be contracted by humans when fine airborne water droplets known as an aerosol, become contaminated.

Where does legionella come from?

Most people catch Legionnaires' disease by inhaling the bacteria from water or soil. Older adults, smokers and people with weakened immune systems are particularly susceptible to Legionnaires' disease.

Although it originates from natural sources, Legionnaire’s disease can be fatal! The disease is contracted through the inhalation of small water droplets that are contaminated; this is usually spread through domestic fittings such as showers.

Why do I need to manage legionella risk?

Duties under the Health and Safety at Work etc Act 1974 (HSWA) extend to risks from Legionella bacteria and the Control of Substances Hazardous to Health Regulations 2002 (COSHH) provide a framework of actions designed to assess, prevent or control the risk from bacteria like Legionella.

The duty is to conduct a risk assessment and prevent exposure to legionella. However, where prevention is not possible there must adequate controls p ut in place to reduce the risk and these must be maintained.

How to manage the risk from Legionella in your property:

Legionella risk assessment
Identify and Assess the Risk

The first step towards ensuring your property is safe from Legionnaire’s disease is to identify and assess the risk of Legionella. It is a legal duty for Landlords to assess the risk of Legionella exposure in their properties, and also to control this risk. 

Manage the Risk

Once the risk of Legionella in your property has been identified and assessed, the second step in the process is to begin the process of managing the risk. This will involve implementing the recommendations from the risk assessment, selecting contractors to maintain the system and arranging for routine monitoring as required.

Prevent and Control

It is important to note that the spread of Legionnaire’s disease is very much preventable. The best way to prevent Legionella is to reduce the amount of stored water.

The HSE describe a typical ‘low risk’ example as a small domestic-type water system, where daily water usage is sufficient to turnover the entire system; where cold water is directly from a wholesome mains supply (no stored water tanks); where hot water is fed from instantaneous heaters or low volume water heaters (supplying outlets at 50 °C); and where the only outlets are toilets and wash hand basins. The best approach to prevent the risk is by eliminating the conditions that allow Legionella bacteria to grow and disperse.

Where the risk cannot be prevented through elimination it must be adequately controlled. One of the main ways to do this is to control the temperature. Low temperatures (under 20°C) allow the bacteria to survive but prevent them from multiplying, temperatures over 60°C cause the bacteria die. Other control strategies can involve reducing the release of water spray, keeping the water and the system clean, and ensuring there is enough flow to prevent the water from going stagnant.

Keep Records

You must keep a record of it so that you can evidence the actions taken to eliminate or reduce the risk. Maintaining a waterlog book for the building can be a useful way of recording water temperatures and other checks to demonstrate that you are managing risks appropriately. Need a water log book, contact us

Practical steps to manage legionella risk

Temperature controls

Legionella bacteria thrives at temperatures between 20 oC and 45 oC. Below 20 oC, the bacteria won’t die but will remain dormant. If the temperature is over 50 oC, this will kill the bacteria.

Store hot water above 140°F (60°C) and maintain circulating hot water above 120°F (49°C). Store and maintain circulating cold water below the growthrange most favourable to Legionella (77–113°F, 25–45°C). Note that Legionella may grow at temperatures as low as 68°F (20°C).

In hot water systems, water should be supplied at 60 oC or more so that any bacteria are killed.

If the system is one with re-circulating hot water, then it’s important to make sure that the hot water never comes out of the taps at less than 50 oC (55 oC in healthcare environments), and the cold water is always below 20 oC.


It’s important that you only fit showers in areas where they will be used regularly, at least once a week.

If showers aren’t being used regularly, then they should be flushed through (at least once per week) to eliminate the risks of stagnant water and the growth of bacteria. It’s also good practice to have a programme for dismantling, cleaning and descaling all shower heads at least quarterly, as this will help to prevent bacterial growth.

Stagnant water

Water stagnates when it stands unused for prolonged periods. Stagnating water, especially when the temperatures are between 20 oC and 45 oC can create ideal conditions for legionella and other bacteria to start multiplying rapidly. Stagnation is more likely in dead legs and dead ends of pipes where outlets have been removed but the pipework left in place, or in places where water isn’t used often.

Large volume water storage tanks are also a risk factor as water flow and circulation within the tank is often reduced which can lead to stagnation.

A formal legionella risk assessment should be undertaken to identify areas of concern, and then a plan developed to tackle identified risks to prevent legionella growth.

Monitoring your water system's
How can Summit Environmental help with Legionella risk?

Whoever in your company or building has responsibility for legionella control (usually called the legionella responsible person) should ensure the water systems are managed properly, control measures checked and inspected regularly and the systems kept clean and under microbial control.

It’s the company’s responsibility to ensure the responsible person is competent to do their job and this may involve specialist training. They should also have the authority to take any actions they deem necessary to manage the risks from legionella.

When monitoring water temperatures, the hot and cold water outlets which are closest or furthest to the mains water tank or heater are the most important to watch – these are known as the sentinel outlets. Monitor at these points to make sure temperatures are kept within an acceptable range

How can Summit Environmental help?

Temperature checks

Legionella risk assessments

Systems of control

Compliance checks

Water log books

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