||The ACOP says that the risk from the exposure of legionella should be prevented or controlled and that the precautions taken should be monitored to ensure that they remain effective. The following section on monitoring offers guidance on how to achieve this in hot and cold water systems.All water services should be routinely checked for temperature and water demand, and inspected for cleanliness and use. Ideally, the key control parameters should be monitored by a building management system if one is present. This will allow early detection of problems in maintaining the control regime.The frequency of inspection and maintenance will depend on the system and the risks it presents. All the inspections and measurements should be recorded and should include:
This should comprise the following:
Routine microbiological monitoring of hot and cold water systems using dip slides or TVCs is not necessary since systems will be totally enclosed, i.e. they are not open to the elements and to significant external contamination (in the same way as cooling towers).
However, there is the potential for micro-organisms to proliferate in various parts of hot and cold water systems. This could manifest itself in taste and odour problems and microbiological investigation should then be carried out. The conditions that supported this microbiological growth could also support legionella growth and so the system should be investigated fully.
Monitoring for legionella
It is recommended that this should be carried out:
Samples should be taken as follows:
The complexity of the system will need to be taken into account in determining the appropriate number of samples to take. For example, if there is more than one ring main present in the building, taps on each ring will need to be sampled. In order to be representative of the system as a whole, samples should be of treated, circulating water and not taken from temporarily stored water, e.g. at TMV – controlled taps and showers. These may require sampling but this should be determined by risk assessment, e.g. where such fittings are used in areas where susceptible individuals may be exposed (see paragraphs on flushing of such fittings).
Analysis of water samples for legionella should be carried out by a UKAS accredited laboratory, which takes part in the PHLS Water Microbiological External Quality Assessment Scheme for the Isolation of Legionella from Water. The interpretation of any results should be carried out by experienced microbiologists. Table 4 gives guidance on action to be taken if legionella is found in the water system.
Action levels following legionella sampling in hot and cold water systems
Legionella bacteria (cfu/litre)Action required
More than 1000Either:
If the majority of samples are positive, the system may be colonised, albeit at a low level, with legioella. Disinfection of the system should be considered but an immediate review of control measures and risk assessment should be carried out to identify any other remedial action required.
The system should be re-sampled and an immediate review of the control measures and risk assessment carried out to identify any remedial actions, including possible disinfection of the system.