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Methods for the Examination of Waters and Associated Materials |
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1.2.2 Artificial aquatic habitats
There is now ample evidence to show that bacteria of the genus Legionella are ubiquitous in artificial water systems, especially in warm waters (30 - 35°C).
- Urban environmental isolates were first detected in waters collected from air conditioning cooling towers and evaporative condensers (10).
- Legionella species can also be present in other water systems and have been found in tap waters, shower waters, hot water tanks and on the inside surfaces of shower heads.
- They have also been shown to be present on flexible seals (for example rubber gaskets) and metal surfaces within plumbing systems used in domestic potable water supplies (11).
- Isolates have been cultured from water collected from showers and from nebulizers as well as from domestic water supplies (12, 13).
- When spa pools are inadequately maintained, conditions can support growth of legionellae and other micro-organisms which may then become aerosolised and possibly inhaled (14) by members of the public.
Legionellae, if present within protozoa, can survive the usual concentrations of chlorine and/or other disinfectants commonly used to treat potable water supplies; hence legionellae may remain present in potable water.
Domestic hot waters, especially if below 55°C, may contain large numbers of Legionella bacteria.
- In addition to water temperature, the materials and design of plumbing systems also seem to play an important role in the growth of these organisms.
- For example, the presence of nutrient sources such as plasticisers in synthetic rubber gaskets, plastic pipes and hoses, and the presence of dead-legs or blind-ends can support the growth of legionellae, as can obstructions to, or stagnation in, water flow.
- In addition, the presence of biofilms or slime layers containing other background bacteria, protozoa, and algae on the surface of pipes contribute to the growth of these organisms.
Legionella pneumophila can survive for prolonged periods of time in tap waters but do not grow or multiply unless supported by other organisms (15).
- Although Legionella pneumophila has been isolated from water at temperatures ranging between 7 - 58°C, the bacteria only multiply actively (13) between 20-45°C.
- A minimum temperature of 60°C is required to kill Legionella bacteria in hot water systems.
| Format adapted by T2 Scientific© 2005 |
t2.200.1.v1.0 |
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Source: Blue Book 200 Part 1 downloaded 27 May 2005 |