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the most environmentally friendly protection against leigonella and other water-borne bacteria

About Legionella and other Water-Borne Bacteria

Water-borne bacteria

Water is prone to bacteria growth when it enters a building’s plumbing. 

Biofilm, also known as ‘slime’, is an aggregate of micro-organisms which provide a home for bacteria to grow and multiply. 

Complex piping networks, like those in hospitals, hotels and large residential buildings, are especially prone to bacteria growth.

The disease-causing (pathogenic) bacteria include Pseudomonas aeruginosa, Helicobacter pylori, E. coliand Mycobacteria avium and Legionella.
If water is not contaminated, Legionella and other conditions like Ecoli, will not occur.

Incubation may take up to two weeks. Initial symptoms are flu-like, including fever, chills, and dry cough. 

Advanced stages affect the gastrointestinal tract and the nervous system. Other advanced symptoms of pneumonia may also present.


Legionella pneumophila thrives in temperatures 20-45°C.

Legionnaire’s Disease acquired its name in July 1976 when an outbreak of pneumonia occurred a convention of the American Legion in Philadelphia. 

Legionella is a detectable bacteria. Non-detection is not an acceptable excuse for Legionella in public buildings.

For more information about Legionnaire’s disease, please click here.

Modes of transmission

Drinking water is not the only way harmful bacteria can enter the human body. Bacteria can be inhaled in droplets while showering, brushing teeth or washing.

Even while washing hands, droplets can become airborne directly from the faucet or after water splashes against the sink.

Water droplets can enter the lungs and cause infection also by aspiration.

All four modes of transmission (ingestion, inhalation, aspiration and skin contact) have one crucial fact in common – water.

Reducing the risk of Legionella and other water-borne bacteria

1. Thermal 
(i.e. controlling legionella by constant hot water)
Increased scaling in calorifiers and biofilm in the water system provides nutrients for Legionella, which cannot live above 60°C. However, it is difficult to maintain constant temperature levels on the hot water return. 

To prevent scalding at water outlets, thermostatic mixing valves (TMVs) are required, although TMVs themselves can act as breeding sites for Legionella and other bacteria. TMVs are also expensive to service and maintain.

To protect a water system against Legionella and other bacteria by maintaining the water supply at over 60°C, and then using TMVs to achieve lower temperatures for day-to-day use, is a needless waste of energy (and money).

2. Chemical
Hazardous chemicals, including sodium hypochlorite (chlorine), can disturb rather than remove biofilm, risking subsequent outbreaks.

Legionella and other water-borne bacteria can hide in scale and biofilm, which is not penetrated by most chemicals. Indeed, after chlorination, bacteria can re-emerge.

Chlorine can ‘gas out’ and dissipate at warmer temperatures, compromising effectiveness in the water system. Furthermore, the chemicals used in water systems are toxic and hazardous as well as antisocial in taste and odour.

Compliance with hazardous substance regulations (COSHH) is expensive.

3. Ionisation
The cost of copper-silver ionisation can be set against the cost of thermal and chemical options making Tarn-Pure ionisation systems the most cost efficient – and environmentally friendly – method of attacking legionella and other water-borne bacteria.

They are also the most effective.

Click here for a further details of ionisation.