3.1.1 Survey of Water Systems

The choice of sampling point location requires a detailed knowledge of the topography or “lay-out” of the water system to be examined, and a thorough understanding of the ecology of the organism. 

• Thus, prior to taking any sample, it is essential to undertake a survey of the site to be investigated to establish the nature of the system and all equipment that utilises water or generates aerosols. 

Routine sampling should only be undertaken following a risk assessment that includes a full survey of the water system. 

In outbreak investigations, there may be no reliable information available on either the “lay-out” of the system or conclusions of previous risk assessments, or indeed, knowledge of whether any risk assessments have been carried out. 

It is not the purpose of this publication to describe the process of carrying out a risk assessment in detail, as this is dealt with elsewhere (4, 7). 

• However, during outbreak investigations, the survey may involve some elements of a risk assessment, in order to support the outbreak investigation and the health and safety interests of sampling staff.

All surveys follow a basic pattern. 

The source and the quality of the water should be determined and the site should be examined to establish the location of all systems using water. 

These systems should then be reviewed and assessed to determine which systems contain water at temperatures likely to support the growth of Legionella bacteria. 

• In addition, areas within the systems where growth of Legionella bacteria may be expected to be greatest should be reviewed, as should locations where potentially contaminated water might produce aerosols or where aerosols might be released into the environment. 

The route or pathway of the water through the system should be followed from its entry into the site to the point where it is used or discharged. 

If a schematic diagram does not exist or is not available, or is known to be or is suspected of being out of date, then an up to date diagram should be prepared indicating, for example locations of: 

• in-coming water supplies, whether of mains or private source;

• storage tanks, expansion or pressure vessels, filters, booster vessel pumps and strainers;

• water softening or other storage or treatment facilities;

• calorifiers or water heaters;

• type and nature of materials and fittings, for example taps, showers, water closet cisterns, valves, thermostatic mixer valves, pressure release valves, bathroom radiators and towel rails connected to the domestic water supply (and associated pipe-work) and the presence of metals, plastics, jointing compounds etc;

• evaporative cooling towers and condensers or heating circuits;

• air conditioning systems or humidifiers within the building which are supplied with, and store, water and which may produce aerosols;

• other equipment that contains water and which might be a potential risk, such as spa pools, humidified display cabinets, machine tools, fountains, etc;

• equipment that is used infrequently or might not normally be of concern but presents a risk only when the system undergoes maintenance or repair; and

• the presence of dead-legs or blind-ends.

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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