The presence and growth of Legionella species in thermostatic shower mixer taps: an exploratory field study

“Legislation in the Netherlands requires routine analysis of drinking water samples for cultivable Legionella
species from high-priority installations. A field study was conducted to investigate the presence of
Legionella species in thermostatic shower mixer taps. Water samples and the interior of ten thermostatic
shower mixer taps were investigated for cultivable Legionella species. In seven cases, Legionella species
was found in at least one of the samples. In four cases, Legionella species was detected in the biofilm
on the thermostatic shower mixer taps interior, with the highest values on rubber parts, and in five cases
in the cold supply water. These results show that thermostatic shower mixer taps can play a role in
exceeding the threshold limit for cultivable Legionella species, but the cold supply water can also be
responsible.
Practical implications: This study showed that contamination of thermostatic shower mixer taps
(TSMTs) with Legionella spp. was frequently observed in combination with contamination of the water
system. Consequently, a combined focus is necessary to prevent the proliferation of cultivable Legionella
spp. in TSMTs. In addition, the results also demonstrated that biofilms on rubbers inside the TSMT had
high numbers of Legionella spp., probably because rubber contains relatively high concentrations of biodegradable
substrates. Therefore, improvement of the rubber materials is necessary to reduce the proliferation
of cultivable Legionella spp. in TSMTs.”

(Citaat: van Hoof, J., Hornstra, L.M., et al. – The presence and growth of Legionella species in thermostatic shower mixer taps; an exploratory field study – Building Services Engineering Research Technollogy 35(2014)6, p.600-612)