How to build-in legionella prevention

27th October 2015

Effective legionella prevention must begin at the specification stage, with building designers and installers aware of the risks associated with some modern trends. Water saving, for example, while undoubtedly good for the environment, presents a particular problem, with low flow taps allowing water to stagnate, creating the right conditions for Legionella to grow.

In hot and cold water systems, the risk areas that support the growth of harmful bacteria are controllable with good design, followed by ongoing operation and maintenance. Some examples include:

  • Dead legs and capped pipes can cause stagnation and should be avoided where possible, and flushed out regularly if unavoidable.
  • Low use water outlets should be installed upstream of frequently used ones – eg a seldom used shower installed upstream of a frequently used toilet.
  • Cold water systems should be maintained, where possible, at a temperature below 20 °C.
  • Hot water should be stored at least at 60 °C and distributed so that it reaches a temperature of 50 °C (55 °C in healthcare premises) within one minute at the outlets.
  • Combi boilers should not allow hot water to enter the cold water space. The thermostat must be set as close to 60C as possible and hot water to the taps, should be at a minimum of 50C.

Value engineering

Other problems occur when ‘value engineering’ techniques have been employed that don’t, in our opinion, present a good enough solution. Cost-effective ‘fit and forget’ water treatment solutions, such as magnetic water conditioners, are often favoured due to their low energy and low maintenance credentials. Problems usually present themselves several months or years after commissioning, due to the fact that lime-scale formation is not controlled throughout the entire water system as effectively as with traditional salt-based water softeners.

We see many examples of supplementary treatment devices that end up failing or being turned off all together due to a lack of understanding in terms of their required Planned Preventative Maintenance (PPM) regimes or their importance – training is key, for all members of the building services and facilities management team.

There are non-chemical alternatives to water treatment, such Guardian’s Wallenius AOT, a photocatalytic water purifier which greatly reduce bacterial levels in the water, without the use of biocides. Where chemicals are used, by tailoring dosing to a specific system and its usage, excess dosing can be avoided.

By building in legionella control from the outset, ongoing maintenance should be easier, with less problems and greater equipment longevity. We can help, find out about our water system construction services here, or contact us for more information.