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Management of Water Systems

Management of Water Systems

The Legionella bacteria is commonly found in domestic water systems. The bacteria favour water temperatures between 20°C & 45°C and proliferate where nutrients are available. The bacteria remain dormant below 20°C and will not survive in water temperatures above 60°C.

Using temperature control

The primary method used to control the risk from Legionella is water temperature monitoring.

Water systems should be operated at temperatures that prohibit the growth of Legionella bacteria, for example

  • Hot water storage cylinders (calorifiers) should store water at 60°C or higher
  • Hot water should be distributed at 50°C or higher (thermostatic mixer valves need to be fitted as close as possible to outlets, where a scald risk is identified).
  • Cold water should be stored and distributed below 20°C.

All water systems should be routinely monitored by a competent person to ensure compliance, the ‘sentinel’ outlets (furthest and closest to each asset) would be identified in the legionella Risk Assessment for monthly checking of the distribution temperatures. In addition, all stored hot water temperatures should be monitored every month and cold storage vessels at least every six months

Stagnant water favours Legionella growth. To reduce the risk you should remove dead legs/dead ends in pipe-work, flush out infrequently used outlets (including showerheads and taps) at least weekly and clean and de-scale shower heads and hoses at least quarterly. Cold-water storage tanks should be cleaned periodically and water should be drained from hot water cylinders to check for debris or signs of corrosion.

Design systems to minimise Legionella growth, by:

  • Using materials that do not encourage the growth of Legionella.
  • Keeping water systems as short and direct as possible
  • Ensuring structural compliance by fitting tanks with tight fitting lids, lid vents, overflow insect screens and adequate insulation.
  • Ensuring minimum water storage and maximum water usage

Other control methods

Other methods to control Legionella include copper and silver ionisation and biocide treatments (e.g. chlorine dioxide). To ensure that they remain effective their application will need suitable assessment as part of the overall water treatment programme including proper installation, maintenance and monitoring.

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