Legionella is a bacterium that causes the disease known as legionellosis or Legionnaires’ disease. The disease can develop when people inhale the bacteria, for example in a shower or via a misting system. Symptoms range from a mild fever to pneumonia.

Conditions that promote the growth of Legionella bacteria include:

• stagnant water

• water temperature between 20°C and 50°C; the optimum temperature is 35°C–46°C

• acidity (pH) between 5 and 8.5

• sediment that leads to the formation of a biofilm

• presence of micro-organisms, such as algae, flavobacteria, Pseudomonas and amoebae.