Stagnant water systems can support the growth of legionella, these can then be released in an aerosol spray which can result in respiratory infection if inhaled. To avoid this the water system should have been flushed on a weekly basis. If this is not the case and your premises has been closed for more than 1 month, the following measures are recommended:
- Flush out the system – please refer to the guidance to understand how to do this without risk of infection
- Disinfect to 50ppm of free chlorine or equivalent biocide
- Run water heated to 60C through the whole water system
- Carry out a risk assessment
Further guidance can be found in the Charter Institute of Environmental Health new guidance document: Legionnaires’ disease: lockdown risks and reopening safely or the Health and Safety Executive's information on Legionella risks during the coronavirus outbreak.