Ultrafiltration instead of reverse osmosis - an alternative?

Reverse osmosis systems have also conquered private households in recent years. By contrast, ultrafiltration equipment is much less common. Do you offer a real alternative to further purification of the drinking water?


Ultrafiltration filters out all foreign matter and contaminants from the water through ultrafine pore membranes. This process is a physical process. It takes place without residues and without the use of chemical agents.

The pore size in the ultrafiltration is between 0.01 microns and 0.05 microns. These are orders of magnitude in the range of one to five hundred thousandths of a millimeter. In practice, tubes made of ceramic or plastic are used, which have an inner diameter of about 0.5 to 2 mm. These tubes are arranged in bundles, which ensures that even larger amounts of water can be filtered. By bundling many individual tubes, a sufficient flow rate is achieved.

What is interesting about this pore size, above all, is that pathogens are also reliably filtered out. Bacteria usually have a size of 0.5 μm to 1.5 μm, even smaller germs such as the Bacterium subtilis (0.3 μm) are still reliably retained. So it will be filtered out:

  • all substances whose molecules are larger than 0.05 μm
  • all bacteria
  • all protozoa, antraxpores, etc.

Also foreign substances contained in the water can be safely and reliably removed up to a molecular size of 0.05 microns. This applies in particular to cloudy substances and surface-forming substances that adversely affect the taste and color of the water.

However, salts and minerals dissolved in the water are retained. Only a few types of viruses can pass through the filters, since viruses are between 15 and about 500 nm in size, so much smaller than bacteria.

Reverse osmosis systems

By contrast, reverse osmosis systems work according to a different principle. They produce ultrapure water that is free from all foreign substances, but also from salts and minerals. Upstream is usually a carbon filter, the water quality ever improved so far that the membrane is protected, and has a higher performance.

The ultrapure water produced by reverse osmosis contains no minerals and salts. It is comparable to distilled water. On the other hand, there are serious medical concerns when drinking.

Conversely, if the system is adjusted so that salts are retained, this, in turn, is at the expense of the filter effect.

Comparison of both methods in practice

Ultrafiltration reliably and safely removes all pathogens and contaminants of higher molecular size from tap water. Only a few types of viruses can still be present in the water, but in a greatly reduced concentration. The technology is simple and not very susceptible and is also suitable for continuous use - it is not for nothing that ultrafilters are also used for trekking.

A disadvantage of reverse osmosis systems is that a biofilm of bacteria can form on the membrane, which are retained, but find a rich supply of nutrients. They multiply strongly there and can break through production or use-related defects in the drinking water. That means a high risk. Add to that the medical effect.

Reverse osmosis systems are also more expensive to buy, require more energy and have a very high water consumption (up to ten times the amount of drinking water taken). In addition, osmosis water can attack stainless steel and other delicate materials, as it reacts very aggressively like distilled water.

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