A significant number of people at the American Legion convention in Philadelphia in 1976 became ill with pneumonia-type symptoms. As this was where the disease was first identified, it became known as Legionnaires’ disease. The bacteria are a serious concern in any building with a water system. This blog will explore the question of how does Legionella grow. The conditions that allow it to spread, the most common sources of contamination and how to prevent outbreaks. Whether you’re managing a commercial facility and are responsible for health and safety or just a homeowner wanting to protect the health of your family and friends, this guide will offer insight into how to reduce the risk of Legionella in your water system.
What is Legionella?
Legionella bacteria, identified as Legionella pneumophila, are the cause of Legionnaires’ disease and Pontiac fever, a milder form of the disease. The bacteria are found naturally in freshwater environments, such as rivers, ponds, lakes and even water fountains and features, where they are relatively harmless to human health. However, the bacteria become hazardous when they grow in man-made water systems, as if tiny droplets of the water contaminated with the bacteria are inhaled, for example, in a shower, they cause the disease. Legionnaires’ disease is particularly dangerous for the elderly and those with lowered immune systems, specific health issues or even current or former smokers.
How does Legionella grow?
Stagnant water
Slow-flowing or stagnant water provides perfect conditions for the Legionella bacteria to grow. If water remains still, disinfectant levels drop, and biofilms can develop. This means the temperature can settle into the band, which is optimal for the bacteria to grow. That’s why taps, pipes or sections of a water system that aren’t in frequent use are at a high risk of bacterial growth.
Poor maintenance of systems
Water systems that aren’t regularly maintained can become breeding grounds for Legionella bacteria. Tanks, pipes and showerheads that aren’t frequently used can develop scale, corrosion and biofilms, which means that disinfectants in the water are lowered or non-existent, creating perfect conditions for the bacteria to colonise.
System design issues
Older buildings which have had modifications to the water heating system can have poor water system designs, including ‘dead legs’, or sections of pipe that have been capped and have no flow through them. These and overly complicated plumbing layouts, as well as infrequently used taps and showers, can trap water and promote bacterial growth.
Optimal temperature range
What temperature does Legionella grow at? The ideal range is between 20°C and 45°C. At what temperature does Legionella grow rapidly? The most rapid growth is at around 37°C, close to body temperature. Below 20°C, the bacterial growth is slowed down significantly and above 60°C, the bacteria begin to die. This is why monitoring the water temperatures of your taps and tanks is vital to prevent the growth and spread of the Legionella bacteria.
Presence of nutrients
Water has many components, even after it has been treated and sent through municipal systems to our properties. Organic matter, such as rust, algae, limescale and biofilms in our water systems, can all act as nutrients for bacteria. Pipework corrosion and poorly filtered water can all increase the amount of nutrients in the system, creating a perfect environment for the bacteria to develop and multiply over time. How long does Legionella take to grow? Under ideal conditions, colonies can develop within a matter of days, which is why regular monitoring is vital.
The most common sources of Legionella growth
Legionella can rapidly grow in many environments, as long as the conditions are right, especially in places where water is stored, recirculated and especially aerosolised. Systems where still or slow-moving water is combined with nutrients, such as limescale, rust or other organic matter, especially if it’s within the ideal temperature range, are likely to develop dangerous bacterial colonies. Without monitoring and control in place, these places can rapidly become a highly dangerous situation, especially for those who are medically vulnerable. Some of the most common sources of bacteria include:
- Hot and cold water systems, especially in large buildings
- Cooling towers and evaporative condensers such as those for air conditioning (AC)
- Spa pools and hot tubs
- Decorative water features and fountains
- Industrial water systems and manufacturing equipment
- Large AC or HVAC (Heating, Ventilation and Air Conditioning) systems with water-based cooling
- Showerheads and tap outlets
- Windscreen wiper tanks of a vehicle
In short, any system that stores or recirculates water and creates any kind of water spray, vapour or aerosol can become a source if it’s not properly managed and monitored.
How to prevent Legionella from spreading
Regular management and monitoring of the places where Legionella may commonly be found can help to contain and control the risk of the bacteria from spreading and posing a threat to the health of the building’s occupants. Some of the best practices to prevent the spread of Legionella are:
- Temperature control: Make sure your hot water tanks are kept above 60°C and that cold water remains below 20°C.
- System flushing: Regularly flush outlets in rooms that aren’t frequently used, such as taps and showers, to prevent the water in the pipes from stagnating.
- Regular cleaning and disinfection: Consistent removal of scale, biofilms and other sediment from tanks and pipework is essential.
- Water treatment programmes: Chemical dosing, such as chlorine dioxide and filtering systems, maintains the quality and disinfection of the property’s water.
- Risk assessments: Carry out regular, routine Legionella risk assessments in compliance with ACoP L8 (Approved Code of Practice for Legionnaires’ disease) and HSG274, the Health and Safety Executive’s technical guidance.
- Routine monitoring and record keeping: Document water temperatures, disinfection levels and any maintenance or treatment activities that show compliance.
Anyone considered a duty holder, such as employers, landlords and those in control of premises, is legally responsible under the ASoP L8 and HSG274 regulations to manage the risk of Legionella bacteria in the property they’re responsible for, as failure to comply can lead to legal consequences.
Why should you seek professional support?
Managing the risk of Legionella is so much more than simply turning up the heat on the hot water tank and flushing out taps every now and then. It requires a deep understanding and knowledge of plumbing system design, microbiological risks and a grasp of the strict legal responsibilities of ACoP L8 and HSG274 guidance. It also means identifying problem areas and optimal growth zones, and the maintenance of complex compliance records.
Water hygiene specialists, such as our team at H2O Hygiene, are trained to identify risks you might miss, conduct comprehensive risk assessments, recommend system improvements for your unique site and complete the relevant records for legal compliance. The expertise of professional water hygiene specialists offers legally defensible protection for your organisation.
Not managing the risk of Legionella properly can result in serious health risks, especially for vulnerable people, such as the elderly or those with weakened immune systems. An outbreak could result in substantial fines and even corporate manslaughter charges or criminal prosecution under health and safety laws. Partnering with a professional team who are up to date with all legal guidance and can tailor solutions to your facility, sector and organisational needs is the smart way to stay compliant and protect your people.
Do you require Legionella support? Get in touch and book your Legionella risk assessment today!
Without wishing to scaremonger, Legionella thrives in the right conditions and can pose a serious threat to health. But with the proper monitoring and maintenance, you can stop it from spreading. Whether you’re responsible for an office, school, care facility, hospital or industrial site, your water systems must meet strict health and safety compliance standards. Our team of expert, trained and certified specialists can carry out a comprehensive risk assessment, recommend tailored solutions, maintain your records and help ensure you stay compliant with the legislation.
Speak to one of our water hygiene experts and book your Legionella risk assessment or remedial works today, giving you peace of mind that your system and people are compliant and protected. Call us on 01922 666108 or email [email protected].
