3.1.2.2 Physico-Chemical Conditions 

One of the most important factors for the growth of Legionella is the presence of other bacteria and the availability of nutrients for their growth. 

These may be derived from contamination within the system, or the use of materials of construction that supports growth; this applies particularly to non-metallic components. 

• For this reason, only approved materials and fittings (47) should be used. 
• Natural organic materials should not be used in construction or in repairs. 

Other organisms growing within the system may encourage the growth of Legionella bacteria and react with biocides. 

• Hence, there should be no obvious signs such as algae or other plants growing in the system, or layers of slime in tanks or on other visible surfaces.

To support the growth of Legionella bacteria, the temperature of the water should be in the range of about 20 - 45°C (optimum conditions being between 30 - 40°C) for at least some of the time. 

• The pH and ionic composition of the water also need to be compatible for growth to occur. 

• In practice, water of potable quality will always be capable of supporting the growth of Legionella bacteria. 

• Similarly, water used for most industrial purposes will support the growth of Legionella. 

• Biocides may be added to control microbial growth, and if so, the condition in the system, including other chemicals that may be in use, should not inhibit their operation or activity. 

• Extraneous material may interact with biocides, thus, reducing their effectiveness, and biofilm, corrosion or scale formation will provide a protective environment for the growth of Legionella and other micro-organisms.

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Format adapted by T2 Scientific© 2005	t2.200.1.v1.0
	Source: Blue Book 200 Part 1 downloaded 27 May 2005