Hotels and other business have been warned to flush out the water supply in their buildings before reopening to prevent the potentially deadly Legionella bacteria from spreading.
Guidance published by Public Health England (PHE) advises "regular flushing" of the water system at premises such as dental practices, hairdressers, gyms and hotels, as well as office buildings, to stop bacterial growth.
They are also required to carry out a detailed review of all aspects of their water management system before reopening following the coronavirus lockdown.
Legionella, which is naturally present in water systems, causes Legionnaires' disease, which is fatal in 10% of cases.
It can cause serious illnesses in people over the age of 50, smokers and those with underlying health conditions.
The bacteria multiply when the temperature of water is between 25C and 50C or if there is poor or no flow into the system.
As many hot and cold water systems will not be running, the chances of the bacteria forming will increase if no action is taken, especially during the warmer months.
The PHE guidance said: "Regular flushing out of the premises' water system throughout the shutdown period is required.
"However all aspects of the water management system need to be reviewed before reopening the business, and necessary action will be dependent on the complexities of the system.
"This may be done by a combination of workers employed by the organisation if they have the necessary skills and knowledge.
"However, if a water system requires disinfection then a water consultant will be needed."
People who think they may have Legionnaires' disease are advised to visit nhs.uk/conditions/legionnaires-disease/ or to call 111.
