LEGIONELLA - World Health Organization

4.4.2 Monitor control measures
This step involves defining the limits of acceptable performance and how these are monitored.
Routine monitoring of a potable water distribution system will include surrogate observations,
such as:
• turbidity
• disinfectant residual
• copper and silver ions
• structural integrity of the system
• temperature.
A thermometer and a surface probe are useful for measuring water temperatures at each part
of a system, at outlets representative of the “worst case scenario” (i.e. at the points at which
the risk is likely to be highest). Such outlets — often termed “sentinel points” — might include
the furthest point from the water heater in a hot-water system, or the incoming water in a
cold-water system.
The results of tests such as those listed above allow corrective actions (discussed in Section 4.5.1,
below) to be taken to protect public health.
Tests carried out for legionellae and heterotrophic colony counts in the distribution system do
not give timely information on the performance of the system, and are therefore most useful
in validation and verification.
4.5 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
• prepare management procedures (Section 4.5.1)
• establish documentation and communication procedures (Section 4.5.2).
4.5.1 Prepare management procedures
This step involves preparing management procedures, including corrective actions, for normal
and incident conditions. Corrective actions include repairing defects, and possibly re-treating
or discarding water that might be contaminated, to ensure that unsafe water is not supplied.
Table 4.3 gives examples of values used as levels to trigger corrective action for Legionella in piped
water systems in different countries. These values are generally used to support risk assessment
or to monitor the effects of control measures.
LEGIONELLA AND THE PREVENTION OF LEGIONELLOSIS