Closed up businesses and offices could increase the risk of legionella…


A variety of internal and external factors can lead to a Legionella problem in your building where water is contained (detailed below).

By following the below steps, you can help reduce the risk.

How to address Legionella growth

When there is a reduction in disinfectant levels in your building water systems, Legionella can grow. Your building water supply may need long-term supplemental disinfectants added to the water to boost the level of disinfectant and help limit Legionella growth.

Legionella grows best within a certain temperature range (25°c-42° ). To keep water outside the range for Legionella growth, it is important to keep cold water cold and keep hot water hot.  It is important to maintain water heaters at appropriate temperatures while following anti-scald regulations. Sometimes maximum temperatures allowed may be too low to limit Legionella growth. Engineering controls that mix hot and cold water together at or near the point of use can reduce the risk of scalding while allowing water in pipes to remain hot enough to limit Legionella growth.

When water does not flow well, the resulting areas of stagnation encourage biofilm growth, reduce water temperatures to levels that allow Legionella to grow, and reduce levels of disinfectant. It is important to understand the flow of water in your building in order to identify areas of risk where water may become stagnant.

Maintaining and operating your building’s equipment effectively will help prevent biofilm, organic debris, and corrosion from contaminating your water system; all of these provide a habitat and nutrients for Legionella.

It is important to monitor external factors that may affect the water entering a building and increase the growth of Legionella in complex water systems. Construction, water main breaks, and changes in municipal water quality are all important factors to consider.

Where Legionella can grow or spread

Legionella can grow in many parts of building water systems that are continually wet, and certain devices can then spread contaminated water droplets. Some examples of devices where Legionella can grow and/or spread through aerosolization or aspiration (when water accidentally goes into the lungs while drinking) include:

  • Hot and cold water storage tanks
  • Water heaters
  • Water hammer arrestors
  • Expansion tanks
  • Water filters
  • Electronic and manual taps
  • Aerators
  • Tap flow restrictors
  • Showerheads and hoses
  • Pipes, valves, and fittings
  • Centrally installed misters, atomizers, air washers, and humidifiers
  • Nonstream aerosol-generating humidifiers
  • Infrequently used equipment including eyewash stations
  • Ice machines
  • Hot tubs
  • Decorative fountains
  • Cooling towers
  • Medical equipment (such as CPAP machines, hydrotherapy equipment, bronchoscopes)
How can National Maintenance help?

 Prevention is better than cure, so we wanted to share with you some measures that can be adopted to create water systems that are hostile to the growth of legionella. Traditionally, temperature is used to control legionella and should wherever possible be the first act of defence.


Temperature control

Cold Water – Cold water should be stored below 20°C and distributed to all outlets within two minutes of opening the tap below 20°C then the cold water circuit will not encourage bacterial growth including legionella growth.

Hot Water – Hot water should be stored at 60°C and distributed and supplied to all outlets above 50°C within 1 minute of operation.

Stagnation: Stagnation can be prevented by introducing routine flushing programmes and reducing the volumes of stored water.

A Legionella risk assessment is required to cover water systems in any commercial premise. This includes rented housing particularly where communal services are present.  We would always recommend an annual review to ensure the systems are being safely managed. But if you’ve had changes to the water systems the risk assessment will need to be updated.  As well as an annual review our skilled and qualified team can also deliver a monthly maintenance service.

National Maintenance
National Maintenance

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