Hot and cold water systems in buildings that are empty or with under occupancy must address the issue of stagnation:

If the building is still partially in use:

  • If possible, drop stored water levels in tanks to maintain <24 hours storage
  • Flush to simulate use – weekly flushing may not be sufficient
  • Monitor temperature to ensure thermal gain in cold water is controlled
  • If fitted, consider temporarily increasing levels of potable water treatment dosing – consider other consequences of this such as corrosion and make the decision on balance of benefit
  • If controls are lost (temperature, biocide levels, etc.) the guidance in HSG274 is to sample for legionella weekly
  • Consider other short term measures to keep remaining occupants safe such as point of use filters at designated locations with other areas shut off

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