Minimising the risks of legionellosis #2

Schools and academies operate a wide variety of equipment which either supplies water, or relies on a supply of water, to function.

These include hot and cold water plumbing; showers; toilets; hand basins; swimming pools and spa baths; spray humidifiers, air washers and wet scrubbers; water softeners; horticultural sprinklers, hoses and misting systems; lathe and machine tool coolant systems; vehicle washes; and fountains and water features.

All of this equipment must be assessed and maintained regularly in order to minimise the risk of infection by the legionella bacteria, which can cause a fatal form of pneumonia when inhaled in aerosol form. The risk is heightened in stagnant conditions and where the water within a system is stored between 20 – 45 degrees centigrade.

Here is a breakdown of the steps that must be taken, and at what intervals, to ensure the safe operation of all water-based systems within a school environment:


  • Check that hot water is being stored above 60 degrees centigrade
  • Check filters in spa baths and swimming pools, and backwash any sand filters.
  • Check water treatment in spa baths and swimming pools three times a day, and treat with an oxidising biocide.


  • Inspect and flush shower outlets for 2 minutes. If the shower has not been used within the last 7 days run through a bucket of water to ensure no spray is generated.
  • Flush through any little-used water outlets such as toilets and taps before use, again taking care not to generate any spray.
  • Clean and disinfect the entire spa bath or pool system.
  • Confirm the effectiveness of any non-chemical water treatment in spray humidifiers, air washers and wet scrubbers.
  • Clean and disinfect the resin and brine tank of any water softeners according to manufacturer’s instructions.


  • Check and record the temperature of water in the water heater flow pipe. It should be greater than 50 degrees centigrade.
  • Check and record the water temperature of the first and last taps on hot water circulating systems. Taps should reach 50 degrees centigrade within one minute of being opened.
  • Where localised thermostatic mixing valves are in use, a contact thermometer should be used to check and record the temperature of the water at the supply point of the valve. It should be 50 degrees centigrade.
  • Check and record the water temperature of the first and last taps on a cold water circulating system. Water should be below 20 degrees centigrade after running the water for up to 2 minutes.

NB. Competent personnel should locate the correct taps and valve supply points for inspection in all hot and cold water systems. In addition, according to the Approved Code of Practice under the COSHH Regulations 2002 temperatures in both hot and cold systems ought to be recorded every month. 


  • Maintain a storage temperature of 60 degrees centigrade for one hour in systems supplying hot water through local electric water heaters.
  • Dismantle, clean, disinfect and descale shower heads and hoses.


  • In cold water systems check the water temperature furthest away from the ball valve is less than 20 degrees centigrade , and that water flowing from the valve is also lower than 20 degrees centigrade.
  • Clean, disinfect and descale spray humidifiers, air washers, wet scrubbers, and lathe and machine tool coolant systems.


  • Conduct a professional inspection of the internal surfaces of water heaters, and remove all scale and sediment.
  • Ensure cold water tanks are suitably lidded or sealed to prevent contamination.
  • Clean, disinfect and descale pipe work, spray heads, make up tanks and all wetter surfaces of horticultural misting systems.

The next blog will contain practical guidance on checking water temperatures within the school environment.

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