The hidden danger


Legionella bacteria may be present in any drinking water, because this type of water is not sterile. They can survive in water temperatures below 20° C, but cannot proliferate. Infection in humans occurs when water droplets contaminated with Legionella are inhaled, or when water containing Legionella accidentally enters the trachea. You can find out more about Legionella here – where it comes from, who is at risk, and how to safeguard against infection.


BWT can provide the following solutions for disinfecting drinking water:

BWT Disinfection


What is Legionella?

There are more than 40 different types of Legionella bacteria and over 60 serologically distinct groups have been identified to date. Legionella pneumophila serogroup 1 is mainly responsible for infections in humans.


There are two types of disease:

  • Legionnaires’ disease or Legionellosis is a severe form of pneumonia which, when treated early enough, has a mortality rate of 20%, but this rises to 80% if left untreated.

  • Pontiac fever has symptoms similar to ‘summer flu’ and does not require hospitalisation.


Where does Legionella occur?

As drinking water is not sterile, Legionella can occur in any type of drinking water. The bacteria can survive in water temperatures below 20° C, but cannot proliferate.


Conditions for proliferation:

  • Water temperatures of 20° C-50° C and a pH value of 5.0-8.5. Optimum conditions for proliferation are water temperatures of between 35° C and 45° C.

  • Biofilms in pipe systems: Legionella are absorbed into the biofilms of protozoa, i.e. amoeba, and multiply by an intra-cellular process. Other microorganisms that live in biofilms provide vital nutrients to sustain the Legionella.

  • A supply of nutrients such as hardness components (Ca2+, Mg2+), iron compounds (corrosion products) and organic substances, i.e. amino acids (cysteine).

  • Hot water installations are at particular risk.


Who is at risk?

Basically, anyone can become infected with Legionella, but the following groups are at greater risk:


  • Individuals under stress • People travelling

  • Older individuals (50+ years old )

  • People suffering from an illness, particularly those infected with HIV, who have had organ transplants or are receiving chemotherapy

  • Heavy smokers

  • People with high alcohol consumption

  • People which chronic pulmonary ailments


How can it be prevented?

Construction, operational and procedural measures must be taken in the planning, implementation, operation and maintenance of drinking water systems to prevent the growth of Legionella. This includes taking account of the quality of the drinking water supplied and the installation, operation and maintenance of the water treatment systems that serve to protect the installations from sludging, limescale deposits and corrosion.


BWT offers a range of water treatment products and processes for the control and prevention of Legionella:

  • Particle protection
    Filtration of the drinking water is both standard and necessary in drinking water installations to inhibit the proliferation of Legionella. Users can therefore prevent the sludging of boilers and pipes and pitting corrosion.


  • Limescale protection
    Limescale deposits can lead to increased roughness on the interior of pipe surfaces on which the biofilms develop and where the Legionella can multiply. Legionella also need calcium and magnesium ions as nutrients, and so the formation of biofilm and the nutrients that sustain the Legionella can be minimised by implementing limescale protection systems.


  • Corrosion prevention
    Corrosion can lead to deterioration in the cleanliness of drinking water and increases the roughness of the interior pipe surface that encourage the development of biofilms. The iron compounds produced by corrosion are also important nutrients for Legionella. The dosing of agents that prevent corrosion, or alternative corrosion protection, can prevent particle and limescale formation and also inhibit the growth of Legionella.