Legionella Monitoring of Cooling Towers & Cooling Water Systems
All legionella monitoring and sampling programmes for cooling towers and cooling water systems should include routine sampling and testing for the presence of bacteria. The water testing procedures should include for both general (aerobic) bacterial species and more specifically legionella bacteria.
Since the detection of legionella bacteria requires specialist laboratory techniques, routine monitoring for aerobic bacteria, usually carried out with dip slides, can be used as an indication of whether microbial control is being achieved in the cooling water system.
Recommended frequency for legionella monitoring & sampling
In addition to the regular sampling for aerobic bacteria in cooling water, a routine monitoring scheme should also include periodic sampling for the presence of Legionella bacteria. This should be undertaken at least quarterly, unless sampling is necessary for other reasons, such as to help identify possible sources of the bacteria during outbreaks of Legionnaires’ disease.
More frequent monitoring, including sampling should be carried out when commissioning a cooling water system and establishing a water treatment programme. Legionella monitoring, specifically water sampling should be carried out on a monthly basis, until it can be shown that the system is under microbial control.
Cooling towers, legionella positive results & what to do
If a legionella positive sample is returned from the laboratory as a result of routine water sampling, more frequent samples may be required as part of the review of the system risk assessment, to help establish when the system is brought back under control.
In the UK the Health & Safety Executive recommend that the sampling method should be carried out in accordance with ISO 11731:1998 and the biocide neutralised where possible. All water samples should be taken as near to the heat source as possible.
They should be tested by a UKAS accredited laboratory that takes part in the Public Health Laboratory Service Water Microbiology External Quality Assessment Scheme for the isolation of egionella from water.
The laboratory should also apply a minimum theoretical mathematical detection limit of less than, or equal to, 100 legionella bacteria per litre of sample.
Interpretation of test results
Legionella bacteria are commonly found in almost all natural water sources, so sampling of water systems and services may often yield positive results and the interpretation of any results of sampling should be carried out by experienced microbiologists.
Failure to detect legionella bacteria should not lead to the relaxation of control measures and monitoring. Neither should monitoring for the presence of legionella bacteria in a cooling tower or cooling system be used as a substitute in any way for vigilance with control strategies and those measures identified in the legionella risk assessment.
Specialist water quality analysis services
Legionella Control International offer a comprehensive range of UKAS accredited legionella testing, sampling and laboratory analysis services capable of undertaking an extensive range of analyses including those for legionella, E.coli O157, Pseudomonas and others.
Our professional lab services can also be used for the testing and microbial analysis of samples to assist in the identification of food poisoning bacteria including Salmonella, Listeria, E.coli O157, Campylobacter and Clostridium perfringens.
Expert legionella monitoring & support
For further information and expert assistance regarding legionella monitoring, risk management and compliance issues please call +44 (0) 161 877 0586 to speak to one of our specialist advisors or send your questions to us here.