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2.2.03 Pathogens in taps – an underestimated problem

Even top-quality drinking water can still be contaminated in the last few metres before it emerges from the tap: poor-quality seals and hoses are a bacterial paradise – this can have serious consequences for people with a weakened immune system under certain circumstances. A new research project is currently investigating how to improve the hygienic safety of drinking water installations.

How does drinking water get to the consumer? It travels a long way to get there, from the waterworks through the pipelines and into the home, strictly monitored and kept at peak quality – until it reaches the water meter. “This is when it hits a grey area: the home installation. A highly visible variety of materials undergoing little control can be used here, some of which represent a paradise for micro-organisms”, says Professor Hans-Curt Flemming of the University of Duisburg-Essen. Drinking water is not sterile and indeed should not be – it still contains bacteria that survive even with a lack of nutrients and are completely harmless. The key to success in waterworks is extracting the nutrient base for the bacteria. This produces “stable drinking water”. “When these ravenous germs come across materials that provide them with food, then it’s like paradise to them. They don’t need much to thrive – small amounts of exuded softener, colouring, antioxidant and other products added to plastics are perfectly sufficient. They establish themselves there and form thick biofilms in which pathogens can settle, grow, then be flushed out to contaminate the water”, continues Flemming.

Then even the best water loses its level of quality, all in the last few metres on the way to the tap. What circumstances cause this? Are there any epidemics? What level of monitoring is there? Which materials are authorised? How can problems be avoided?

Hot water systems tested

These questions were the main focuses of the large-scale study funded by the BMBF called “Biofilme in der Hausinstallation (biofilms in home installations), which ran from October 2006 to March 2010. Five research facilities and 17 industrial partners spent four years examining these questions under the co-ordination of Professor Hans-Curt Flemming (University of Duisburg-Essen and IWW Mülheim). The results were certainly worth attention: “The statistical analysis of more than 20,000 measurements taken by health authorities showed that legionella was present in over 13% of the hot water systems tested”, said Professor Thomas Kistemann from the Institute for Hygiene at the University of Bonn, one of the researchers involved. One particularly unpleasant pathogen is Pseudomonas aeruginosa, which causes inflammation of the lungs, urinary tract infections and also especially persistent infections of burns. This was found in 3% of the tests performed. Kistemann goes on: “Since monitoring was made mandatory four years ago, only half the public buildings and hotels affected have been tested. That is not to say that the authorities have not been active, simply that they are overwhelmed and understaffed. And who is responsible for water quality in multiple dwellings? Experience shows that anyone taking on this task quickly becomes unpopular.”

Evidence of Pseudomonas aeruginosa through cultivation (left column, blue) vs. fluorescence in-situ hybridisation (FISH) (right column, purple)

Evidence of Pseudomonas aeruginosa through cultivation (left column, blue) vs. fluorescence in-situ hybridisation (FISH) (right column, purple)
Evidence of Pseudomonas aeruginosa through cultivation (left column, blue) vs. fluorescence in-situ hybridisation (FISH) (right column, purple)
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Shower hoses – a bacterial paradise

The scientists were able to use true-to-life model systems to demonstrate that shower hoses and also relatively small seals become a paradise for bacteria when they contain materials that support germ growth. Biofilms could be spotted on some of them after one or two weeks – even with the naked eye. The usual suspects in such cases are plastics that no test has approved for use with drinking water. Low-cost taps often contain additives for biological use such as softener or remains of release agents, or become contaminated with substances during production and installation. An unfavourable combination of poor material quality (e.g. low-cost taps) and water quality encourages strong biofilm development – and thus provides a living environment for pathogens. “That does not necessarily mean that epidemics are going to break out, but illness could occur and lead to time off work and a temporary loss of quality of life”, says Professor Kistemann. “When the immune system is weakened, e.g. after an operation, critical situations can arise”, says Professor Martin Exner from the University of Bonn.

Computer-controlled, semi-technical home installation for long-term testing with true-to-life consumption profiles

Computer-controlled, semi-technical home installation for long-term testing with true-to-life consumption profiles
Computer-controlled, semi-technical home installation for long-term testing with true-to-life consumption profiles
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So what can be done? Firstly, it was demonstrated in the research project that the current monitoring methods need to be expanded on considerably in problem cases. It has been shown that the pathogens being sought can go into a sort of coma, which causes them to disappear from the radar of standard methods. However, they wake up as soon as their living conditions improve and can be just as infectious as they were before. Practical problem cases were able to demonstrate the benefits of new molecular biology methods for identifying the causes of persistent bacterial contaminations and eliminating them.

Greater attention towards home installations

One conclusion from this successful research project is to dedicate more attention to home installations, as this is where even the best water can lose its quality. “We have drawn up important notes on methods to prevent this”, concludes Hans-Curt Flemming. However, it was clear that there is still a great need for research and regulation – not only for materials but also for the testing procedures. The last few metres before the tap are crucial, and yet amazingly underexposed.

As a result of the findings from this project, the consortium has drawn up a research proposal that addresses the problems in detail. It particularly focuses on the temporary disappearance of pathogenic germs from the monitoring radar and their sudden recurrence, the conditions under which this occurs and how the hygienic safety of drinking water installations can be ensured. The proposal was successful and will receive over EUR two million total funding from September 2010 to August 2013.

University of Duisburg-Essen
Essen Campus – Biofilm Centre

Prof. Dr. Hans-Curt Flemming
Universitätsstrasse 5
47141 Essen, Germany
Tel.: +49(0)2 01/83-66 01 1
Fax: +49(0)2 01/183-66 03
E-mail: hc.flemming@uni-due.de
Internet: www.uni-due.de/biofilm-centre/index_en.shtml
Funding reference: 02WT1153-1157
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