We use accredited laboratories to carry out biological monitoring programmes, including Legionella testing, Total Viable Count (TVC) and potable water testing.

‍When do I need to sample water for Legionella?

Legionella monitoring should be carried out if any of the following circumstances occur:

• The risk assessment considers it is necessary
• Where there is doubt whether the control measures in place are working effectively
• Systems treated with biocide
• Temperature control is consistently not being achieved
• Disinfectant concentrations are not achieved
• Some high-risk premises where the population have increased susceptibility
• Where there has been an identified outbreak of Legionellosis
• Areas of low usage, stagnation, excess storage capacity, dead-legs, excessive heat loss and cross-flow in water systems

How many samples do I need to take and from where?

If sampling and monitoring for legionella are considered to be the appropriate course of action then the sampling must be carried out following the: BS7592 Sampling for Legionella organisms in water systems code of practice BSI. The number of samples will depend on the complexity of the system.

A representative sample from around the water system will be taken from both hot and cold-water systems. All samples are clearly labelled with the location and whether they were pre or post flushing.

Where to take a sample in Cold water systems

• A sample should be taken from the nearest outlet if the water is a private supply
• The temperature of the incoming mains supply is above 20°C from the cold-water storage tank(s)
• The sample should be taken from the sentinel outlets on each branch of the system

Where to take a sample in Hot water systems

• Samples should be taken from the calorifier hot water outlet and the base of the calorifier where possible
• Sentinel outlets on each branch of a single line system
• Sentinel outlets on each loop of a circulating system

Who can test the samples?

The analysis must be carried out by a UKAS accredited laboratory.

Action levels following a legionella positive result

>100 cfu/l and up to 1000

If the minority of the samples are positive the system must be resampled. If similar results are achieved again a review of the control measures and risk assessment should be carried out to identify the remedial actions required.

If the majority of samples are positive the above actions should be carried out and disinfection of the water system should be considered.

>1000 cfu/l

The system should be resampled, and an immediate review of the control measures and risk assessment carried out to identify any remedial actions. This may include disinfecting the system. Retesting should take place several days after the disinfection and at frequent intervals afterward until control is achieved and maintained.

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