Bushwalk Australia

Katadyn web page mentions:

Due to their tiny size, viruses can theoretically not be removed with a 0.2 micron (or any physical) filter. Nevertheless, long-term experience in the field has indicated that Katadyn Filters can retain viruses. This surprising fact can be explained: Viruses have an electrical surface charge that attaches them to other particles or materials. Therefore, the tight pore-structure of the Katadyn Filters removes the viruses attached to particles from your drinking water.

Has anyone else come across info regarding viruses being filtered out via being attaching to other particles or materials?

etrangere wrote:Due to their tiny size, viruses can theoretically not be removed with.........any physical filter.

They might want to inform Sawyer of this.

Viruses also come in various sizes.

From the CSL website:

Nanofiltration
'Virus elimination or virus filtration (nanofiltration) removes viruses by size exclusion. In particular, filters with a defined small pore size remove viruses with a diameter larger than the pore size. The main advantage of this process is that both enveloped and non-enveloped viruses can be removed without denaturing plasma proteins or affecting the quality of the derived products.'

Now this pertains to preparation of biological agents in a laboratory, not squeezing out drinking water but e principle is the same.

I used to have a First Need filter that claimed to remove viruses electrostatically. There was accompanying documentation as to how completely they were removed. Here is what they say today about this filter: http://generalecology.com/info/techmemocert

Does Katadyn offer similar data?

You can buy syringe filters that are .02 micron pore size. Those will filter out the vast majority of viruses but you'll be thirsty trying to drink through one.