Legionella & Legionnaires Disease

Post-lockdown COVID-19 Legionnaires’ threat.

Legionnaires’ disease is a concern at anytime but particularly at the moment due to the COVID-19 pandemic. With a large majority of the UK’s commercial buildings sitting empty due to COVID-19 social distancing measures, there is potential for an outbreak of Legionnaires’ disease when restrictions are lifted.

From schools, hotels, holiday homes and restaurants to offices and leisure facilities, thousands of buildings are sitting empty across the UK. Business owners and landlords have never had to deal with such low occupancy, and as such, the threat posed by the build-up of legionella bacteria in water systems must become a priority. The Association of Plumbing & Heating Contractors and local councils are amongst those warning that Legionnaires’ Disease could pose a serious public health concern once social distancing restrictions are relaxed, and people once again start to occupy these spaces.

About Legionnaires’ Disease

Similar to COVID-19, Legionnaires’ Disease is condition that affects the lungs. A form of pneumonia caused by the inhalation of small droplets containing the Legionella bacteria, the disease can be potentially fatal. Legionella bacteria is commonly found in water and thrives in temperatures between 20 and 45°C and can be spread in a variety of ways such as hot and cold water outlets, atomisers and wet air conditioning units.

In stored or recirculated water, the bacteria can build up in systems and essentially ‘feed’ off rust, sludge, scale and biofilm that naturally exists in most water systems. Any building that has stood empty for a period of time poses a higher risk as stagnant water within the system provides the ideal environment for growth, and with the country’s recent hot weather, there is a very real threat to thousands of organisations and businesses when the UK reopens for trading. Some Wolseley customers have reported mould growth in water tanks just one week into systems being unused. While the bacteria doesn’t distinguish between residential and commercial dwellings, the risk is higher to commercial buildings at present due to their lack of water usage and turnover throughout the coronavirus pandemic.

Both landlords and employers have a legal duty to assess and control the risks posed by Legionella bacteria, however as a somewhat rare disease, the seriousness of the threat is sometimes overlooked.

Assessing the risk

When closing a business such as a hotel or restaurant for example, landlords or employers should shut down and flush the water system. With the lockdown announcement meaning many businesses were open one day, and forced to close the next, the reality is that many won’t have done this — particularly with the added stresses related to future financial security and the furloughing of staff.

For some systems, such as those on small premises, where water isn’t stored in cylinders, or where hot water is fed from instantaneous heaters, the risk is usually low however it is still important to review the situation.

For buildings which are used by vulnerable people such as those with chronic and acute medical problems or those over the age of 65, extra precaution should be taken. Extra care should also be taken in buildings with centralised hot water systems or buildings with more than 10 stories. Buildings with cooling towers, hot tubs, decorative fountains or centrally installed misters, atomisers, air washers or humidifiers should prioritise the risk assessment.

Taking precautions

There are a number of precautionary steps that can be taken to prevent the build-up of Legionella bacteria, and while it is advised that these measures are taken regularly, they will be even more important when reopening buildings up for public or employee use.

For those responsible for workplace or public safety, ensure outlets used infrequently such as showerheads, fire sprinkler systems, eye wash stations, and taps are flushed out weekly.

Legionella in hot water

Temperature control is the other primary method used to control the risk of Legionella. Bumfords can conduct risk assessment and inspection before your business reopens. They will ensure that the building’s water heater is properly maintained, and the temperature is correctly set:

  Hot water storage cylinders should store water at 60°C or above.

  Hot water distribution should be at 50°C or higher.

  Cold water should be stored and distributed at 20° or below.

  The distribution of sentinel outlets (furthest and closest to each tank or cylinder) should be checked monthly.

  Dead legs from pipework should be removed.

  Hot water storage cylinder temperatures should also be checked on a monthly basis.

  Cold-water tank temperatures at least every six months.

A professional inspection by Bumfords will also ensure pipes and tanks are properly insulated, cleaned and sealed, while confirming the system is free of materials that encourage bacteria growth.


Bumfords can provide a range of solutions to help to minimise the risk of Legionnaires’ disease. Thermostatic mixing taps, valves and showers are one such method and are installed before the water outlet such as a tap or shower. They allow the hot water system to run at a higher disinfection temperature to eradicate Legionella bacteria, then blend with cold water at the point of use to achieve a pre-set safe temperature from the outlet.

The other option is to install an anti-Legionella valve which ensures water circulation is maintained to prevent stagnation and bacteria build-up. These valves are ideal for use with commercial boilers and expansion vessels as water in the pipework of these vessels can be left to stagnate once it gets pushed into the vessel pipes. The valve converts a single connection expansion vessel into a ‘flow through’ type by diverting a portion of the flow into the vessel so that the water is continually renewed.

Splash reduction

Businesses can also install bacterial filters to taps, showerheads and other water outlets. These filters prevent Legionella bacteria from being released by the outlets to which they are fitted. These are particularly common in heath and social care environments where the risk and need to prevent infection is much greater. These filters must be checked to ensure there is enough activity space to minimise contamination from outlet users and to prevent splashback contamination from drains. An example of activity space would be ensuring there is sufficient airspace above a filled basin.

Testing for Legionella

There is a range of Legionella testing kits that will warn users when the bacteria is present in the system. These kits provide results in under 30 minutes without the need for the delays sometimes involved in laboratory testing, enabling businesses and organisations to take immediate action if required.

At Risk Area: Showerheads

Legionella bacteria multiply in water temperatures of between 20-60°C. Shower valves operate between these temperatures making them an ideal breeding ground for the bacteria which can be spread through the shower spray. Regular cleaning and disinfecting of shower heads should take place every three months with a cleaning record kept.

Bacterial Control / Water Treatment

There are a range of water treatment methods that can be applied to a water system to combat bacteria growth. The most popular treatment is probably chlorine. Chlorine dioxide Legionella control is a tried and tested method for the treatment of hot and cold water systems, however there is evidence to suggest that chlorine can cause damage to copper pipes over time.

Other chemical solutions include those from the likes of Fernox which combines hydrogen peroxide containing colloidal silver and other stabilising materials to treat water-borne bacteria and viruses.

Chemicals aside, UV light can also be used as an effective water treatment method. With no negative by-products UV-C light kills Legionella bacteria by disrupting its DNA.

At Risk Area: Showerheads

Legionella bacteria multiply in water temperatures of between 20-60°C. Shower valves operate between these temperatures making them an ideal breeding ground for the bacteria which can be spread through the shower spray. Regular cleaning and disinfecting of shower heads should take place every three months with a cleaning record kept.

Time to act

The need for businesses and landlords to conduct risk assessments, ensure the necessary precautions are taken and fit solutions to reduce the threat of Legionella has never been greater. A Legionnaires’ outbreak is easily preventable with the right knowledge of the threat and solutions available. As buildings reopen for public and employee use, it’s important the risks and precautionary actions are communicated effectively to employers and landlords. Spread the word and prevent the threat.