What is Legionella ?

Legionella bacteria is commonly found in water and especially in purpose-built water systems such as cooling towers, evaporative condensers, hot and cold water systems and spa pools as well as water fountains. Between water temperatures of 20-45°C, the bacteria can multiply whereas it is normally dormant below 20°C and does not usually survive above 60°C.

Legionnaires’ disease is a potentially fatal type of pneumonia, contracted by inhaling airborne water droplets containing viable Legionella bacteria. Such droplets can be created, by hot and cold water outlets, atomisers, wet air conditioning plant, and whirlpool or hydrotherapy baths.

Anyone can develop Legionnaires’ disease, but the elderly and those with cancer, diabetes or chronic respiratory or kidney disease are at more at risk.

So how can Legionella be prevented and what measures need to be undertaken to control and or eliminate the likelihood of catching this life threatening disease?.

First of all, a full risk assessment should be carried out of all hot and cold water systems to ensure adequate measures are in place to control the risks.

The primary control measure would be to check the water temperature from the sentinel taps and ensure:

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

It is recommended that ‘sentinel’ outlets (furthest and closest to each tank or cylinder) are checked at least monthly for the distribution temperatures. The hot water storage cylinder temperature is also checked at least once a month and cold water tank temperatures at least every six months.

Stagnant water which can be prevalent on dead legs favours Legionella growth. To reduce this risk the dead legs should be removed in pipe-work and infrequently used outlets (including showerheads and taps) and flushed at least weekly to clean and de-scale shower heads and hoses.

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.

It is also important to ensure that systems are designed in order to minimise Legionella growth. This can be achieved by:

  • Keeping pipe work as short and direct as possible;
  • Ensuring there is adequate insulation carried out in pipes and tanks;
  • The use of materials that discourage growth of Legionella;
  • Ensuring contamination is prevented for example by fitting tanks with lids and insect screens.

Additional recommended controls should ensure that Water samples are taken periodically and analysed by approved Laboratories to determine Legionella bacteria counts remain at an acceptable level. The testing frequency should be determined by level of risk, in accordance with the risk assessment.

Other methods to control Legionella include copper and silver ionisation and biocide treatments (eg 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.