Why point-of-use sterile water filters are Class I medical devices


Sterile water filters play an important role in hygiene and pathogen reduction at hospitals and other medical facilities. These medical devices are used wherever patients could be at risk because of facultative pathogens in the water system.  Although the drinking water in most parts of Europe is high in quality and tested regularly, it is still possible for bacteria, viruses and other pathogens to occur in the water.  In most cases this is not due to the quality of the water supplied to the system by the water providers but is instead the result of contaminated pipes. The formation of biofilms favours the proliferation of microorganisms. In particular, waterborne pseudomonads such as Pseudomonas aeruginosa, and Legionella bacteria, can cause dangerous infections in weakened people. Because the threshold values used in the regular testing of drinking water supplies are based on healthy people, medical establishments have to put special measures in place.

Focus on patient safety

KRINKO (the commission for hospital hygiene and infection prevention) at the Robert Koch Institute (RKI) has therefore issued special requirements for water provision. It specifically recommends that point-of-use 0.2 µm filters be used in the care of neonates and immunosuppressed patients.


As well as normal water filters, which are also used in private households, there are sterile water filters. These are Class I medical devices and have been specifically designed for use in hospitals and other medical establishments. The pore size of just 0.2 µm enables them to provide reliable protection against waterborne pathogens. In accordance with the FDA definition of sterile filtration, these filters lead to at least 7 log reduction of the test microbe Brevundimonas diminuta per square centimetre of filter area, which is equivalent to reducing the microbe content by 99.99999 %.

Strict quality requirements for the validation of medical devices

“Medical devices are all instruments, apparatus, appliances, software, substances or preparations made from substances or other articles, […], intended by the manufacturer to be used specifically for diagnostic or therapeutic purposes […].” Sterile water filters meet these criteria because their defined purpose is the prevention of infectious diseases.1

CE-marked medical devices can be marketed by medical device manufacturers certified to DIN EN ISO 13485; they are subject to rigorous quality management.

Different aspects are examined in the validation process such as bacterial retention (in accordance with ASTM F838-15a), filter integrity, chemical compatibility, resistance to physical influences, etc. Another important factor in the validation of filters is the service life. This is the time between installation and deinstallation of the filter. Tests measure the length of time for which the filter is able to stop bacteria and examine the reliability with which it prevents or reduces retrograde contamination.


CE-marked medical devices are subject to rigorous quality management. 


Testing and recording are carried out in field studies under real conditions. Hospitals - as operators of water supply systems - have a responsibility to protect their patients. When they use a CE-marked point-of-use sterile water filter, they can assume that all the procedures necessary for quality assurance have been carried out.

Step backwards rather than forwards

One section of a European Commission is making efforts to stop classifying sterile water filters as medical devices, arguing that water filters do not come into contact with injured skin. In no way does this reasoning correspond with the definition of medical devices mentioned above, which does not name actual contact with the skin as a critical factor in their classification. The European-level discussion did not consider the purpose specified by the manufacturer – namely the prevention of diseases. However, the recommendation has no legal character; the responsibility for adopting it, and for deciding how the definition of medical devices is interpreted, rests with the individual countries.


The European-level discussion did not consider the purpose specified by the manufacturer – namely the prevention of diseases.


If, in future, sterile water filters were to stop being classified as medical devices, this would mean that important requirements for their performance and reliability would cease to apply. There would no longer be any form of regulatory guarantee that water filters were able to provide the performance and reliability essential for daily use in health care establishments to prevent harm to patients and others.   Only when filters are classed as medical devices do their manufacturers need to possess a quality management system in accordance with DIN EN ISO 13485.

A change of classification would also have an effect on product liability.  With a “normal” water filter in place, liability in the case of poor performance - in other words the occurrence of infection – would rest with the hospital and not the manufacturer, who under German law (Civil Code, BGB) would only need to provide a replacement product.

Rigorous application of hygiene standards

As our society gets older and antibiotic resistance becomes increasingly frequent in the population, the recommendations for preventing infectious diseases need to be rigorously applied. The aim is to improve hygiene standards in hospitals and other medical facilities still further – not to relax the standards that already exist. Where water filters are concerned, hospitals fall back on sterile water filters, which are classified as Class I medical devices, because they are the only ones meeting the performance and reliability criteria.



1The legal definition in Germany‘s Medical Devices Act (MPG, section 3 no. 10) states that the purpose is indicated by the details provided by the manufacturer about each specific product.