Risk of Legionnaires’ disease from hot water

Risk of Legionnaires’ disease from hot water
19 March 2018

Legionnaires’ disease is caused by a bacteria called Legionella (Scientific name: Legionella pneumophila). The disease was named after one of the members of the American Legion who caught it while attending a convention in Philadelphia in 1976. Legionella is found naturally in fresh water environments, like streams, rivers, freshwater ponds and lakes but it is not normally a cause for concern as the bacteria exists at very low levels.
Legionella only generally becomes an issue when the bacteria is provided with ideal conditions for reproduction. All types of hot water systems irrespective of size, scale and complexity run the risk of exposure to Legionella depending on their stored water temperature and maintenance procedures.
Proliferation of the bacteria

Legionella bacteria can breed very well in warm stagnant water between 25° to 50°C.  The bacteria are dormant below 20°C and do not survive above 60°C. They can easily multiply at temperatures of up to 45°C.

Poor water management is one of the major causes of the disease. Sometimes homeowners reduce the temperature setting on their hot water system in order to conserve energy. While a reduction in temperature conserves energy, it also proliferates the growth of the bacteria. The risk of contamination will increase considerably if the temperature setting is lowered to 49°C or below. The World Health Organisation (WHO) recommends that water be heated and stored at 60°C, however a study conducted by the Canadian Journal of Infectious Diseases, conducted in 211 homes in Quebec showed that even when a hot water tank thermostat is set at 60°C most heaters still remain contaminated as the bottom of the hot water tank remains at a lower temperature of 30°C to 40°C due to temperature stratification. The study also found that the risk of contamination is much lower if these thermostats are set at 60°C.

In other cases, homeowners switch off their hot water tanks when they go on a holiday. In some cases, large water-storage tanks can be exposed to sunlight, which can produce warm conditions favourable to the bacteria.
One of the key benefits of the Harlequin HeatStream range is that the capacity of potable water stored in the tank is much reduced (compared to conventional hot water storage tanks) while producing large amounts of hot water, essentially reducing the risk of Legionella. For instance, the popular 200 Litre HeatStream contains only around 12 litres of potable water compared to 200 Litres in a conventional tank. Heatstream is available in a range of 8 products ranging from 150 to 250 litre capacities and have models compatible with electric, oil, gas and solar thermal heat sources. They are safe, robust, have a long-life with super-fast recovery and are built to suit modern day requirements.
Steps to prevent growth of Legionella  
  1. Hot water storage cylinders should store water at 60°C or higher
  2. Hot water systems should be routinely checked, purged with hot water when safe to do so, inspected and cleaned
  3. Hot water storage cylinder temperatures should be checked every month and cold-water tank temperatures at least every six months
  4. Remove dead legs/dead ends in pipe-work
  5. Flush out outlets such as taps and showerheads that are not used often at least once a week
  6. Clean and de-scale shower heads and hoses at least quarterly
  7. Hot water must be stored at 60°C (recommended by WHO) by ensuring, at least once a day, the temperature reaches at least 60°C in the entire tank.
  8. Conduct regular inspections by a licensed plumber to ensure that the problem is prevented
Fast Facts about Legionella / Legionnaires’ disease 
  1. Legionella can cause Legionnaires’ disease or Pontiac fever. It is collectively known as Legionellosis.
  2. The disease is not generally contagious, but it is possible to contract in rare cases.
  3. It poses a risk to health when water systems aren’t properly designed, installed or maintained.
  4. Large establishments such as hotels, hospitals and offices, are more prone to contamination because they have larger and more complex water supply systems in which the bacteria can spread quickly.
  5. Legionnaires' disease can even be contracted from contaminated showers, sprinkler systems and spas.
  6. Smaller water systems such as those used in homes are not as likely to be infected with the bacteria as larger systems in workplaces and public buildings.
Sources of Information

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