LEGIONELLA - World Health Organization

In certain circumstances, samples may be taken from locations that are not representative of
the bulk of the tower water. It may often be of interest to include sediment in the sample to
be analysed. When investigating a cooling tower implicated as a potential source of legionellosis
infection, it is essential to collect swab samples of biofilm in the sump or basin of the tower.
Timing of sampling for bacteriological analysis is important, particularly when shot dosing
of biocides is used. Sampling is best undertaken just before shot dosing, as this will demonstrate
the “worst case scenario” in the dosing cycle, and may indicate the need for corrective action
in the water treatment or cleaning programme.
Analytical results should be recorded as part of the documentation in the WSP. Records
should be kept for a period in accordance with local or national legal requirements.
Non-microbial tests
In addition to microbial testing, a number of other tests can be carried out on site, using samples
of cooling tower water. Most analyses are for parameters related to control of corrosion, scale
and particulate matter; they include measurements of temperature, pH, conductivity, chloride,
alkalinity, chromate and organophosphonate. Analysis of antimicrobials is generally limited
to oxidizing chemicals such as chlorine, bromine or chlorine dioxide. The concentrations of
non-oxidizing biocide can be determined in a well-equipped chemical laboratory, although
the methods used are often time consuming and expensive. Turbidity may be determined in
a laboratory or on site with a portable turbidity meter.
5.5 Management and communication
This section should be read in conjunction with Section 3.3.3 of Chapter 3. The steps involved
in management and communication are to:
• develop supporting programs (Section 5.5.1)
• prepare management procedures (Section 5.5.2)
• establish documentation and communication procedures (Section 5.5.3).
5.5.1 Develop supporting programs
A supporting programme should be established, to train all operating staff to perform the required
monitoring and maintenance tasks. Also essential is authorization of regular servicing and
data collection by the owner of the building where the tower or condenser is located, or their
nominated representative.
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS