Managing Legionella in Building Water Systems
In the UK all businesses have a legal responsibility to manage the risks from legionella in their workplaces. In this article our water safety experts explain what legionella is, how it can cause Legionnaires’ disease and who is at risk. It then goes on to consider the risk assessment process and how water temperature, minimising stagnant water conditions and good water system design can help control the risks from legionella in building water systems.
What is legionella?
Legionella is a type of bacteria which is commonly found in lots of different water sources and doesn’t in most circumstances cause any problems.
However, at temperatures of between 20-45°C the bacteria can start to grow and multiply, if there are suitable nutrients available.
Below 20°C the bacteria are dormant, and over 60°C they are killed off.
What is Legionnaires’ disease?
Legionnaires’ disease, caused by the Legionella bacteria, is a serious form of pneumonia which can be fatal to humans.
People catch Legionnaires’ disease by breathing in water droplets suspended in the air which contain the Legionella bacteria – the disease isn’t contagious.
These contaminated droplets of water get into the air from a variety of sources including atomisers, hot and cold water taps or shower heads, air conditioning units and cooling towers, and whirlpool spa baths.
Who can catch Legionnaires’ disease?
Anyone has the potential for catching Legionnaires’ disease.
However, it is likely to be far more serious in the elderly, or people who are heavy drinkers, people who smoke, those who are being treated for serious illnesses such as cancer, diabetes, breathing difficulties or kidney problems.
There is lots of information provided on the Health and Safety Executive (HSE) website about managing the risks from Legionnaires’ disease for specific “at risk” groups.
The need for a Legionella risk assessment
Anyone operating a businesses in the UK is required to carry out a full Legionella risk assessment of both the hot and cold water, and any other water systems serving their premises.
Business owners and employers must also make sure that proper control measures are put in place to address the risks from Legionella and Legionnaires’ disease in their work places.
Using water temperature to control Legionella
Perhaps the most important thing which any business can do to control Legionella growth is to monitor and control the temperature of the water in their buildings.
It is crucial to ensure that water services operate at temperatures that impede growth of the bacteria.
- Hot Water Storage Cylinders – also known as calorifiers – these should store water at temperatures no less than 60°C
- Hot Water – should be piped at temperatures of 50°C or higher (55°C in healthcare properties). Thermostatic mixer valves (TMVs) should be installed as close to taps or shower heads as possible, if there is a risk of scalding.
- Cold water – this should be kept at temperatures under 20°C.
The role of the competent person
Someone who has been designated as a “competent person” should be in charge of the routine maintenance, inspection and cleaning of the water systems, carefully following the processes laid out in the Legionella risk assessment.
What is a sentinel outlet?
Legionella risk assessments of a property should also designate the water outlets which are the furthest away and closest to the cylinders or tank.
These outlets are called the sentinel outlets and are the points at which the distribution temperatures should be checked monthly.
Temperatures in the hot water storage cylinders should also be checked monthly to ensure the correct water temperatures are being achieved.
Six-monthly checks are sufficient for checking cold water tank temperatures.
The risks from low flow or stagnant water
Another risk factor for Legionella growth is slow moving or stagnant water in the system.
Reducing this risk factor involves assessing your pipework and removing areas that cause low flow or stagnation including redundant sections of pipework, dead legs or dead ends.
In addition, there should be a programme of flushing outlets, including shower and taps which are not used often, weekly or more often as the risk dictates.
Shower heads and hoses should be disinfected and de-scaled at least every three months.
Hot water tanks should be drained regularly to allow for inspection to verify that there is no build-up of sludge or indication of rust.
Cold water storage tanks should also be drained and cleaned when needed.
Good water engineering design can help to control Legionella
When designing a new water system, inhibiting Legionella growth should be paramount.
Elements of good water system design include the following:
- Choosing as direct and short a route for water pipes as possible
- Installing high levels of insulation on both pipes and tanks
- Choosing materials which have been shown to discourage bacterial growth
- Designing ways of preventing external contamination such as insect meshes, screens or lids to cover open tanks.
Other Legionella controls that can be used
Businesses should also have a process for testing and analysing water samples to make sure that levels of Legionella bacteria are within safe limits.
The intervals between water testing will depend on the risk indicated by the initial Legionella risk assessment.
Alternative methods for controlling Legionella
There are many other methods which can be considered to control the growth of Legionella bacteria, such as treatment with biocide chemicals like chlorine, stabilised silver peroxide, chlorine dioxide, or ionisation of silver or copper.
These control methods only remain effective if they are assessed as part of the overall water treatment programme and are included in the monitoring process.
Expert Water Treatment and Water Safety Solutions
Water Treatment Services provide a comprehensive range of water and wastewater treatment, water quality analysis, consultancy, and water engineering solutions to support business owners and those responsible for the safe and efficient operation of water systems in the workplace.
Contact us today to learn how our water treatment specialists can help you manage your water systems, maintain regulatory compliance, and ensure safe, reliable performance.
With offices in London serving the South and South East England, Manchester (North West), Birmingham (Midlands), Bristol (South West England and Wales), Leeds (North and North East), and Glasgow (Scotland), supported by regional teams of highly trained technicians and engineers, we deliver specialist consultancy, water quality analysis, engineering support, and risk management solutions across the UK and internationally.
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