Sampling for Legionella Bacteria in Water Systems - Code of Practice


Published by BSI, this document provides recommendations and guidance on the sampling of water and related materials for the investigation of the presence of organisms of the genus Legionella. It is applicable to sampling constructed water systems but also gives methods for sampling of biofilms and sediments that might be present. Some of the same sampling principles can be applied to natural water systems.


This British Standard is applicable to the selection of sampling sites and the methods of sampling for the purposes of routine monitoring, validation, commissioning, investigating a problem, or outbreak investigation. Recommendations and guidance on the selection of sampling points are given. The rationale for the selection of sampling points for particular situations is also covered.


This British Standard is intended for use by all those involved in water sampling for legionellae, including those collecting samples on site and those developing water sampling plans and/or directing where samples are taken from, irrespective of the method of analysis adopted.


It is not applicable to the sampling of soils and horticultural potting mixtures.

The document brings together information on likely sources of Legionnaires’ disease, the selection of sampling sites and the methods of sampling for the purposes of routine monitoring, validation, commissioning, investigating a problem, or outbreak investigation. It covers some aspects of risk assessment to facilitate the selection of sampling sites and to minimize the risk to those involved in sampling. However, it does not give extensive recommendations for carrying out a risk assessment or for the role of sampling within the water safety plans as these are covered in BS 8580-1 and BS 8680.


In the UK, outbreaks of Legionnaires’ disease commonly have been associated with evaporative cooling towers and condensers; hot and cold-water systems in buildings such as hospitals and hotels; and spa pools and hot tubs, including those on display. The use of nebulizers or other medical respiratory equipment contaminated with legionellae (usually by filling or washing such items with tap water containing the bacteria) has also been reported to cause infection.


Other sources implicated in outbreaks globally include natural warm spas and hot springs, indoor fountains, horticultural potting mixtures, ultrasonic misting devices used for humidification in healthcare and domestic premises and to humidify food display cabinets in shops and restaurants, pressure washers, air scrubbers, effluent treatment plants, ice machines in healthcare premises, etc. Household plumbing systems have also been implicated as sources of Legionnaires’ disease.


BSI February 2022


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Sampling for legionella bacteria in water systems : code of practice

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