LEGIONELLA - World Health Organization

5.3 System assessment
This section should be read in conjunction with Section 3.3.1 of Chapter 3. The steps involved
in system assessment, some of which are discussed further below, are to:
• assemble a team to prepare the WSP
• document and describe the system (Section 5.3.1)
• assess hazards and prioritize risks (Section 5.3.2)
• assess the system.
5.3.1 Document and describe the system
In documenting and describing the system, all relevant information and documentation should
be compiled. Box 5.2 lists the particular components of a potable water distribution system
that should be assessed.
Box . Components of cool ng towers and evaporat ve condensers to be assessed
Particular components of cooling towers and evaporative condensers that should be
assessed include:
• the quality of water entering the system
• the design of the devices and the distribution system
• nutrient sources
• the population using the system, including any particularly susceptible people
• the management structure
• the competence of personnel responsible for the system.
Once a desktop review of the system has been completed, a sanitary survey or “onsite” survey
should be carried out to verify the system (see Chapter 4 of WHO, 2004).
5.3.2 Assess hazards and prioritize risks
This step involves collecting and evaluating information on hazards and conditions leading
to their presence, to decide which are significant for safety and therefore should be addressed
in a safety plan.
Source water quality — risk factors
The make-up water for a cooling tower or evaporative condenser will usually come directly from
a municipal or well supply. However, sometimes a holding tank is used, which may contain
rust, sludge and sediment. In some very large systems, it may be necessary to use surface water
from lakes, rivers, streams, or reservoirs as make-up water; such sources are usually laden with
microorganisms and nutrients from the environment.
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS