Suggestions that copper pipework helps reduce the risk of the spread of Legionnaires' disease have been strongly refuted by the Drinking Water Inspectorate [DWI].

The UK Copper Board had made this claim in February 2004, citing research by a Dutch water quality research institute, KIWA. In tests which simulated a Dutch domestic hot water system, the study had suggested that water conveyed by copper pipe could reduce the concentration of Legionella pneumophila by ten times when compared with water in cross-linked polyethylene pipes. This was interpreted as having implications for the relative risk of spreading the disease itself.

However, after reviewing the issue in response to this suggestion, the Drinking Water Inspectorate have dismissed the significance of the research. While accepting that copper probably does have a lower potential for biofilm development than some plastic materials, the DWI says:

"There is very little evidence that materials of construction alone have played a significant role in the induction of outbreaks of legionella. It is understood that poor system design and inadequate operating practices were implicated as the main factor in most outbreaks."

The DWI statement goes on to point out that:

"Many UK outbreaks of the disease have occurred in copper plumbed systems. This suggests that the biocidal properties of copper are insufficient to counter poor system design and operation."

Acceptable materials: copper, plastic and stainless steel
The DWI also refers specifically to The Health & Safety Commission's [HSC] Approved Code of Practice and Guidance [Legionnaires' Disease: The control of legionella bacteria in water systems. Health & Safety Commission 2000]. This Code of Practice does stress the need for the use of materials which do not promote microbial growth. In this context, the use of natural rubber, hemp, linseed oil and fibre fittings is specifically prohibited.

The document states that copper, plastic and stainless steel are specified as acceptable materials for hot water supply in the Water Fittings and Materials Directory. Both copper and a number of plastics materials are listed in that directory.

According to the DWI:

"The nomination of a specific product as the material of choice is not consistent with HSC guidance. The guidance also endorses the use of biocides as a control measure, and notes that, where such biocide regimes are used, there is no need for water to be stored at 60 degrees."

Unrepresentative simulation: Dutch water is non-chlorinated
In a further comment on the Dutch research report, DWI noted that the simulated conditions were not representative of UK water supplies:

"In the Netherlands, water supplies are distributed without chlorination. The presence of chlorine in water supplies has been shown to reduce the incidence of legionella in mains water supplies. Because UK water supplies are invariably chlorinated, the relative biocidal impacts of plastic and copper play an insignificant role in the proliferation of legionella within buildings."

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