What is sterile filtered water? What are sterile filters?

The specifications for sterile filtered water are more stringent than the specifications for drinking water. Sterile filtered water is very pure. It is used primarily at medical establishments and in medical production processes. The water is physically filtered through special filters. According to the FDA’s definition, sterile filtered water is water that has passed through a filter with LRV (log reduc-tion value) = 7. This means the filter holds back 99.99999 % of the test organism Brevundimonas diminuta, the smallest of the aquatic bacteria.

Contamination risk in water pipes

Although the water treatment plants in most European countries deliver water whose hygiene is strictly monitored and meets the specifications of national drinking water regulations, it can happen that the water delivered by a tap within a building is contaminated with bacteria or other microorganisms. This is because of the water pipes in the building. Narrow pipes and complex piping systems with dead sections reduce the flow rate and allow the temperature of the water to rise. If there is no flow of water for a longer period of time the water is said to be stagnant.
Stagnant water provides ideal conditions for the formation of biofilms. A biofilm can contain bacteria, amoebae, algae and other microorganisms and provides ideal living conditions for pathogens like Legionella and or Pseudomonas bacteria. These pathogens pose a high infection risk, especially for immunocompromised patients. For this reason, sterile filtered water is used when caring for immunocompromised people.

Point-of-use sterile filtration and inline filters

Point-of-use filtration and inline filter systems are used in many areas within hospitals and other medical facilities. In the case of point-of-use filtration, water from the building’s water system is passed through special filters attached at the point of use (tap, shower head) to produce sterile filtered water. Point-of-use means that no other technical components are present between the filter and the use of the drinking water from a tap. Point-of-use filters are usually membrane filters with a pore size of 0.2 µm. The filters must be suitable for using at temperatures of up to 60 °C and pressures of up to 5 bar because these temperatures and pressures can occur in drinking water installations. Membrane filtration does not alter the chemical composition of the water.

Use of sterile filters

Normally, sterile water filters are produced and packaged under clean room conditions. However, particular applications require the use of sterile filters. Sterile filters are (gamma) sterilised after production and packaging. In this sterilisation process the packaged filters are subjected to irradiation with the radionuclide cobalt 60. Because of its high penetrating power, this process allows the sterilisation of packaged materials of moderate density. Sterile filters usually have a shelf life of 2 years.

This means the filters are sterile: they are, so to speak, sterilised sterile water filters.

Advantages due to flexibility of use

The rapid and easy installation process means that these filters can be used flexibly and can thus reduce the infection risk for patients and medical staff. When pathogens have been found in the water, sterile water filters are installed, for example on the tap or shower, and ensure that pathogens are reliably held back throughout the defined service life. The filters are exchanged regularly: attention should be paid to the service life given by the manufacturer for each filter. Single-use and reusable systems are available depending on the manufacturer. Some of the available filters include a silver- or copper-coated filter outflow for additional microbiological protection against colonisation by pathogens.

In the non-medical domain, water filters are normally used when Legionella bacteria have been found. In this way it is possible to avoid banning shower use in residential complexes or closing sports halls and indoor swimming pools; point-of-use filters can also be used to protect guests at seasonally-operated hotels and holiday centres.

Sterile filtration is also possible in supply systems

Some areas of clinical facilities can benefit from inline filters situated in the supply system. Certain inline filter systems have been specially developed for cold water supply pipes in medical facilities. This technology is very important in the reprocessing of endoscopes, for example. Sterile filtration by means of special inline filters in the supply system of endoscope cleaning and disinfection devices provides effective protection against recontamination during the final rinsing of endoscopes. Inline hollow fibre membrane filters are also used in the pipes supplying water to birthing pools.

Recommendations for the use of sterile filtered water

The WHO recommends point-of-use water filtration to improve hygiene in at-risk areas of hospitals. In Germany, KRINKO (the commission on hospital hygiene and infection prevention at the Robert Koch Institute) has recommended that point-of-use water filters should be used when caring for highly immunocompromised patients. The French Ministry of Health also advises installing 0.2 µm microfilters on taps in high-risk areas. The filters are therefore used in various settings including intensive care units, oncological wards, transplantation facilities and premature baby units. There are also various national recommendations for the use of sterile filtered water in endoscope reprocessing.

Water filtration has proved reliable for everyday use in hospitals

Sterile filtered water is inexpensive and can be used in unlimited quantities, for example for daily personal hygiene or wound irrigation. The prevention of infections is taking on ever greater importance in medical establishments. Filtration can lead to a considerable reduction in the proportion of nosocomial infections caused by waterborne pathogens in clinical establishments; in the medium and long term this means substantial cost savings. For this reason, more and more medical establishments are choosing sterile water filters for effective prevention of infections.


1Legionella and the prevention of Legionellosis”, WHO Press, World Health Organization, Geneva/Switzerland, Editors: J. Bartram, Y. Chartier, JV Lee, K. Pond & S. Surman-Lee, 2007 
2Recommendations of KRINKO (commission for hospital hygiene and infection prevention) at the Robert Koch Institute (RKI) on the care of immunosuppressed patients: „Anforderungen an die Hygiene bei der medizinischen Versorgung von immunsupprimierten Patienten“, Bundesgesundheitsbl-Gesundheitsforsch-Gesundheitsschutz, 53:357-388, 2010 
3Circulaire DGS/SD7A/SD5C-DHOS/E4 n° 2002/243 du 22/04/2002 relative à la prévention du risque ilé aux legionelles dans les établissements de santé, April 22nd, 2002