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While viruses are not commonly encountered in the great outdoors there is no doubt that many areas of the world that we travel, or live within, that are contaminated with viruses (hepatitis A, norovirus, rotavirus, enterovirus, etc.)

In the world of water filtration, there is the need for ever smaller micron levels of filtration in order to prevent viruses from passing through the filter.

What is the required micron level in order to filter out all viruses from contaminated water?

And because there are multiple standards out there, please reference which standard you are basing your data/answer on.

Additionally, because it is a rather important part of micron filtering, be sure to include if the micron level must be absolute or nominal.

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  • There is no way to filter all viruses. Some viruses are just too small, it's impossible (currently) to produce a porous material with holes small enough, Graphene offers a potential solution to this, but currently this is unproven
    – user2766
    Dec 2, 2015 at 10:11
  • @Liam - lack of citation.
    – Abela
    Dec 2, 2015 at 10:14
  • That's why it's a comment...
    – user2766
    Dec 2, 2015 at 10:22
  • "Virus" originally meant anything that could cause disease. The modern usage "virus" is an abbreviation of "filterable virus," which means something that can still cause disease after passing through a filter. In other words, the fact that you can't filter them out was originally the definition of a virus. If you want to kill viruses, you can use UV (steripen) or halogens.
    – user2169
    Dec 2, 2015 at 15:25
  • @ben-crowell it is widely known that a SteriPen (and other UV devices) does NOT kill, they sterilizes (as in spay and neuter your cats and dogs.)
    – Abela
    Dec 3, 2015 at 5:44

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Let's look at the absolute here.

The hepatitis B virus is 0.042 microns in length; this is about as small as viruses get (http://www.who.int/csr/disease/hepatitis/whocdscsrlyo20022/en/index2.html). This is the standard for "small". The smallest virus known to cause disease in humans is Parvovirus B19, which is 20 nm in diameter.

The best water filters you can get are rated at around 0.001 microns (NF membranes). According to the CDC, they have very high effectiveness against viruses (http://www.cdc.gov/healthywater/drinking/travel/household_water_treatment.html). Some will get though because of a bad pore or mechanical weakness.

But a perfect NF system will block all viruses (that aren't floating strands of DNA/RNA); imagine trying to push yourself through a hole 400x smaller than you. It's not going to happen.

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