Water Sampling

Microbiological monitoring of domestic hot and cold water supplied form the mains is not usually required, unless the risk assessment or monitoring indicates there is problem.

Legionella monitoring should be carried out where there is doubt about the efficiency of the control regime or it is known that recommended temperatures, disinfectant concentrations or other precautions are not being consistently achieved throughout the system.

When Legionella monitoring should be considered

Water systems treated with biocides where water is stored or distribution temperatures are reduced. Initial testing should be carried out monthly to provide early warning of loss of control. The frequency of testing should be reviewed and continued until such time as there is confidence in the effectiveness of the regime.

  • Water systems where the control levels of the treatment regime, e.g. temperature or disinfection concentrations are not being consistently achieved. In addition to a thorough review of the system and treatment regimes, frequent testing, e.g. weekly, should be carried out to provide early warning of loss of control. Once the system is brought back under control as demonstrated by monitoring, the frequency of testing should be reviewed.
  • High risk areas or where there is a population with increased susceptibility, e.g. in healthcare premises including care homes;
  • Water systems suspected or identified in a case or outbreak of Legionellosis where it is probable the incident control team will require samples to be taken for analysis.

Where monitoring for Legionella is considered appropriate in hot and cold water systems, sampling should be carried out in accordance with BS7592 “Sampling for Legionella organisms in water and related materials.” The complexity of the system will need to be taken into account to determine the appropriate number of samples to be taken. To ensure the sample is representative of the water flowing around the system and not just of the area downstream of the fitting, samples should be taken from separate hot and cold outlets rather than through mixer taps or outlets downstream of TMVs or showers. Samples should be clearly labelled with their source location and if collected pre – post flushing.

In both hot and cold water systems, samples should be taken:

  • If considered necessary by the risk assessment;
  • From areas where the target control parameters are not met (i.e. where disinfectant levels are low or where temperatures are below 50°C (55°C in healthcare premises) for hot water systems or exceed 20°C for cold water systems)
  • From areas subject to low usage, stagnation, excess storage capacity, dead legs, excessive heat loss, crossflow from the water system or other anomaly.

In cold water systems, samples should also be taken if required:

  • From the point of entry (or nearest outlet) if the water is supplied from a private water supply or where the temperature of the incoming mains supply is above 20°C from the cold water storage tanks.
  • From the furthest and nearest outlet on each branch of the system (far and near sentinel outlets)

In hot water systems, samples should also be taken as required:

  • From the calorifier hot water outlet and from the base of the calorifier, if it is safe to do so, as some systems are under considerable pressure.
  • From the furthest and nearest outlet on each branch of a single pipe system (far and near sentinel outlets)
  • From the furthest and nearest outlet on each loop of a circulating system (far and near sentinel outlets)

Legionella Bacteria (cfu/l)Recommended Actions
>100 cfu/l and upto 1000 Either

· If the minority are positive, the system should be resampled.
· If similar results are found again, a review of the control measures and risk assessment should be carried out to identify any other remedial action required.
· Disinfection of the system should be considered.
>1000 cfu/l· The system should be resampled and an immediate review of the control measures and risk assessmtn carried out to identify any remedial actions, including possible disinfection of the system.
· Retesting should take place a few days after disinfection and at frequent intervals afterwards until a satisfactory level of control is achieved.