Towards a water-wise world Annual report 2014


Rubber in thermostatic shower mixing valve is source of Legionella

11 June 2014Research

Legionella is regularly detected in the water from thermostatic shower mixing valves, for instance, in hospitals and hotels. KWR research shows that on the rubber in the valves a biofilm can form, which contains an accumulation of Legionella bacteria. The client, UNETO-VNI, makes use of these results to incite suppliers to develop new sealing materials.

“The picture of the presence of Legionella in collective water distribution installations is not a simple one,” says Paul van der Wielen, leader of the study into thermostatic shower mixing valves. “The valves are not the only place where Legionella bacteria grow. We’ve also found them in the installations themselves.” During the course of the study, researcher Luc Hornstra analyses the inner parts of used thermostatic shower mixing valves, among other things. A variety of Legionella bacteria grow in the cultivated samples of biofilm taken from the rubber components. The dangerous, and sometimes fatal, pathogen Legionella pneumophila has not been detected.

Biofilm sampling on various valve components

Biofilm sampling on various valve components

Market alternatives

One of the occasions at which the research results have been presented to the market players is the Nationaal Congres Sanitaire Technieken (National Congress for Sanitary Techniques). Eric van der Blom, the chairperson for the day at the congress and policy staff member at UNETO-VNI, says that he “certainly expects that the suppliers of shower mixing valves will do something with the results. They pay close attention to product improvement. The supplier that comes up with alternatives to the problematic rubber will gain an edge in the market. And if the supplier, while solving the mixing valve problem does the same for other installation components, then several birds would be killed with one stone.”

“I expect that the suppliers of shower mixing valves will do something with these results”

Leading Legionella knowledge

Interest in the pathogen grew following the Legionella outbreak in Bovenkarspel in 1999. But KWR had already built up significant in-house Legionella expertise before that time. “The questions were automatically directed to us,” says Van der Wielen. “And it has remained that way.” Thus KWR has developed DNA techniques to detect and characterise the pathogenic Legionella pneumophila bacteria in water. Moreover, it has established what circumstances favour the growth of the bacteria, such as the influence of the pipe material and of the quantity of degradable material in the water. “Besides its leading knowledge,” says Van der Blom, “KWR is also a particularly pleasant partner to work with. Their project management is well organised and they think along with you.”

Culture plate with Legionella bacteria

Culture plate with Legionella bacteria

The need for research into Legionella’s origin

But there are still a number of questions surrounding Legionella. When a person is infected with the pathogenic Legionella pneumophila strain, the source tracing practically never produces a match with the strain. “This means that we still don’t know where the pathogenic Legionella actually comes from,” says
Van der Wielen. “That is a research question for the future. We think the cooling towers might be involved. In years with a hot July and wet August, one observes an increase in the occurrence of legionellosis cases. The warmed up cooling water in air conditioning units, which operate at full power in July, is an excellent breeding ground for Legionella bacteria. When the hot period is followed by a wet one, the bacteria have little trouble surviving in the air. Research should tell us whether we need to modify our cooling towers regulations.”

© 2018 KWR Watercycle Research Institute

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