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How to Reduce Legionella Growth in your Business

Posted by Chloe on Nov 27, 2019 4:13:21 PM


Legionella is a pneumonia-causing pathogen, which if inhaled by humans, can lead to fatal respiratory diseases. It is naturally occurring and widespread in natural water sources but can lead to explosive outbreaks of Legionnaires’ disease and Pontiac fever when it enters man-made systems. If water systems, such as cooling towers, whirlpool spas, air misters and showers are not well maintained they can soon become serious biological hazards, putting customers, staff and the general public at risk.

This potentially fatal infection is contracted when aerosols and water droplets, which are contaminated with Legionella, are inhaled by humans. Men, the elderly, smokers and individuals with a weakened immune system are far more prone to infection however, the pathogen can affect anyone.

In recent years, there has been a rapid increase in cases of Legionnaires’ disease worldwide, with reported incidences in the US growing at an alarming 500% since 2000. Similarly, between 2000 and 2015 cases of infection in Europe have risen by 347% and 2017 saw the largest ever number of reported cases (9,238) and deaths (574)1.

To reduce public health risk and minimise negative business impacts such as shutdowns, bad press and dramatic fines it’s important to implement water system controls. Below we’ve listed our top tips for limiting Legionella growth in your business or industrial water systems.


Download our 10 Top Tips Checklist for Reducing Legionella in your Business


1. Create a schematic of your system

It is vital that you have an up to date and accurate schematic of your building’s water systems so that you can identify risk areas on your premises and monitor them. Ensure improvements and updates to your schematic when maintenance and changes occur. This schematic will allow you, a trained responsible person or a consultant to assess and identify and risk areas in your systems where further action or increased monitoring may be necessary.


2. Train and appoint a responsible person

UK Legislation (ACOP L8) states that in order for a business’ to properly manage the risk of Legionella, the people in charge of managing this risk must be trained and competent and they must have access to proper advice and information.

ACOP L8 also states that a lack of training is one of the biggest factors contributing to outbreaks of Legionnaires’ disease and has made it clear that training should be a part of the precautions taken by managers to keep themselves, their staff and their customers safe. UK Legislation (COSHH and the HSW Act) also states that employers are expected to implement control measures to reduce the risk of an outbreak. They are required to keep themselves, their staff members and the public safe by providing sufficient information, instruction and training about Legionella and Legionnaires' disease2.


3. Implement and Maintain Water Temperature Controls

Studies have shown that at temperatures above 50 degrees Celsius, Legionella rapidly declines. The UK Department of Health and Social Security Code of Practice states that hot water should be stored at temperatures above 60 degrees Celsius and that returning water should be maintained at 50 degrees Celsius. They also state that cold water should be maintained at temperatures below 20 degrees Celsius to minimise and discourage growth.

In other words, ensure your water is not within the range of 20 and 45 degrees Celsius. If there are areas in the system where maintaining high/ low temperatures is impossible, dosing of the system should be considered.


4. Remove Dead Legs and Prevent Stagnation

Areas of stagnation, such as dead legs and outlets which are not in regular use, can promote the growth of biofilm and Legionella growth. Biofilm can in turn promote the growth of Legionella bacteria and other microbes by supplying them with a host, nutrients and protection from chemical treatment. These areas should be removed where possible or flushed at regular intervals.


5. Treat Your Water System

 Water systems can be treated with a range of biocides, copper and silver ionisation, UV and Ultrasound technology. Treating and disinfecting your water system will kill and inactivate Legionella and other bacteria in your system and will help to minimize growth of biofilm which supplies Legionella with protection and nutrients.

It is useful to mention that a recent study comparing presence of coliform bacteria in water systems using free chlorine residual against chloramines found that the presence of coliform bacteria was 35 times higher in free chlorinated systems than in systems using chloramines. Past research theorises that chloramines may be more successful at infiltrating biofilms to reach Legionella bacteria and other microbes which are protected inside, while free chlorine is limited in its ability to penetrate biofilm due to its faster reaction rate. In effect, free chlorine diffuses before it can successfully permeate biofilm and access bacterial forms inside3.


6. Choose your Pipe Materials Wisely

Research suggests that the material make up of your pipes and any resulting corrosion can greatly influence the effectiveness of biofilm and bacterial control in water systems. For example, corrosion in iron pipes can influence the efficacy of chlorine-based biocides and encourage Legionella growth3.  

A study recently showed that corrosion has a more significant effect on free chlorines ability to infiltrate biofilms and neutralise bacteria, however in this study both free chlorine and monochloramine’s efficacy were negatively impacted. Thus, introducing corrosion inhibitors in systems where pipework material is prone to corrosion could improve biocide efficiency and reduce corrosion rates3.

It has also been shown that biofilm formation was faster on iron pipes than of plastic PVC, even when corrosion control is adequate. Iron also supports more diverse microbial populations that plastic PVC.

Other materials are often used in pipework the above examples have been used to demonstrate a need to consider those options wisely.


7. Filter your water

Filtration may also be useful in systems where water is recirculated, where system efficiency is critical or where water source quality is poor. Filtration of water entering a system can remove particulates and organic matter, reducing the rates of biofilm formation and Legionella growth.


8. Monitor External Influences

Legionella bacteria can enter water as a result of construction, changes in municipal water quality and water main breaks. In the USA alone, there are approximately 240,000 water main breaks every year causing a loss of around 6 billion gallons of water per day3! Inadequate investment into infrastructure maintenance can aggravate this problem and the result is that Legionella and other harmful bacteria can enter water systems, and under the right conditions, multiply rapidly.


9. Test Frequently

Routine testing is a crucial part of any successful risk management program. It is an important tool for keeping control measures, such as temperature and biocide levels, in check, for reducing risk to people’s health and for saving businesses from huge fines and reputational damage. HSE (Health and Safety Executive in the United Kingdom) advises monthly checking for sentinel outlets, which lie closest and furthest away from water tanks and cylinders; monthly checks for hot storage systems and checks for cold water systems every six months7. If your system presents more risk, due to age or complexity, or if there are vulnerable persons present in your facility, consider testing more frequently.


10. Test for VBNC Legionella

VBNC Legionella is a survival stage the bacterium enters under stressful conditions like shock treatment, starvation, unfavourable temperatures5 and UV treatment6.  In this phase, Legionella shuts down functions like reproduction and may appear to be inactivated7.

However, VBNC Legionella have been proven to have the ability to infect human cells can regain their reproductive abilities when conditions in a system improve, or when in contact with amoebae (found in biofilm or supply water)5 causing rapid reinfection of a system. Unfortunately, VBNC Legionella cannot be detected by the traditional laboratory culture testing method outlined in most Legionella guidance worldwide and thus other methods of testing, like Hydrosense, are needed to support lab culture results and provide protection against existential Legionnaires’ disease and the risk it can create for your business.


Download our 10 Top Tips Checklist for Reducing Legionella in your Business


More like this:

Your Full Guide to a Legionella Risk Assessment 

The Silent Danger your Lab Culture Results are not Detecting




  1. ECDC. (2018). SURVEILLANCE REPORT. Available at: http://bit.ly/2lXQ8eP [Accessed: 08 Feb. 2019]. 
  1. Fench, S. (2015). Eplusglobal.co.uk. Available at: http://bit.ly/2kn62yU [Accessed 21 Nov. 2019].
  2. LeChevallier, M. (1999). The National Academies Press. Available at: http://bit.ly/2kn62yU [Accessed 21 Nov. 2019].
  3. gov.uk. (n.d.). [online] Available at: http://bit.ly/2mfHhFo[Accessed 22 Jun. 2018].
  4. Dietersdorfer E., Kirschner A.K.T., Schrammel B., Stockinger H., Ohradanova-Repic A., Sommer R., Walochnik J., Cervero-Aragó S. (2018) Available at: http://bit.ly/2kslWbs(Accessed 31 Jan. 2019)
  5. Grossi M.R., Dey R., Ashbolt N. J. (2018). Available at: http://bit.ly/2kPTYqb(Accessed 31 Jan. 2019)
  6. Mendis L. Li, N., Trigui H., Oliver J.D., Faucher S.P. (2014). Available at: http://bit.ly/2mid7Bn(Accessed 31 Jan. 2019)

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