General monitoring

Guidance

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:
* the name of the person undertaking the survey, signature or other identifying code, and the date on which it was made (computer records are acceptable); and a simple description and plan of the system and its location within and around the building. This should identify piping routes, storage and header tanks, calorifiers and relevant items of plant, especially water softeners, filters, strainers, pumps and all the water outlets.

Annual check

his should comprise the following:
* Visual inspection of the cold water storage tank to check the condition of the inside of the tank and the water within it. The lid should be in good condition and fit closely. The insect screen on the water overflow pipe should be intact and in good condition. The thermal insulation on the cold water storage tank should be in good condition so that it protects from extremes of temperature. The water surface should be clean and shiny and the water should not contain any debris or contamination. The cold water storage tank should be cleaned, disinfected and faults rectified, if considered necessary. If debris or traces of vermin are found, then the inspection should be carried out more frequently.

* Making a record of the total cold water consumption over a typical day to establish that there is reasonable flow through the tank and that water is not stagnating. This can be done by fitting a temporary water flow-meter over the outlet pipe and recording the consumption. It can also be measured by holding the ball valve supplying the water in the closed position and measuring the rate of water level drop within the vessel. Whenever the building use pattern changes, this measurement should be repeated.
* Draining the calorifier and checking for debris in the base of the vessel. The calorifier should then be cleaned if considered necessary.
* Checking the plans for both the hot and cold water circuits to make sure they are correct and up-to-date - this should be done by physical examination of the circuits, if possible. Plans should be updated if necessary. Ensuring that the operation and maintenance schedules of the hot and cold water systems are readily available and up to date with named and dated actions throughout the previous year. Checking the existing of all water connections to outside services, kitchens, fire hydrants and chemical wash units. Any insulation should be checked to ensure that it remains intact. Any water outlets that are no longer used should be removed.

Microbial monitoring

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:
* in water systems treated with biocides where storage and distribution temperatures are reduced from those recommended (see the section on the use of temperature to control legionella). This should be carried out on a monthly basis. The frequency of testing should be reviewed after a year and may be reduced when confidence in the efficacy of the biocide regime has been established in systems where control levels of the treatment regime (e.g. temperature, biocide levels) are not being consistently achieved. As well as carrying out a thorough review of the system and treatment regime, frequent samples, e.g. weekly, should be taken until the system is brought back under control, when an outbreak is suspected or has been identified (see section on action in the event of a outbreak), or testing for legionella may also be required in hospital wards with 'at risk' patients - e.g. those immunologically compromised.
Samples should be taken as follows:
* cold water system - from the cold water storage tank and the furthest outlet from the tank. Samples may also be required from outlets in areas of particular concern, e.g. in hospitals wards with 'at risk' patients.
* hot water system - from the calorifier outlet of the nearest tap to the calorifier outlet plus the return supply to the calorifier or the nearest tap to that return supply. Samples should also be taken from the base of the calorifier where the drain valves have been fitted. The furthest outlet from the calorifier should also be sampled. Samples may also be required from outlets in areas of particular concern, e.g. in hospital wards with 'at risk' patients.
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 100 but less than 1000
More than 1000Either:
If only one or two samples are positive, system should be re-sampled. If a similar count is found again, a review of the control measures and risk assessment should be carried out to identify any remedial actions.

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.

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