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Legionella testing services

Legionella Testing

Dantek use accredited laboratories to carry out biological monitoring programmes, including Legionella testing, Total Viable Count (TVC) and potable water testing.
Dantek are able to supply a range of water hygiene testing products. For a list of the products on offer please see the  price guide for further details.

Testing for Legionella Bacteria


The HSE advise that routine microbiological sampling of domestic hot and mains fed cold water is not normally required unless a Legionella Risk assessment or routine monitoring shows it is necessary, and other control measures (such as temperature) are unsuccessful at preventing and controlling the risk from legionella bacteria.

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 healthcare premises where population have increased susceptibility
  • Where there has been an identified outbreak of Legionelloisis
  • 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 is 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 and will be advised by Dantek.

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 a 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. Re testing should take place several days after the disinfection and at frequent intervals afterwards until control is achieved and maintained.