Do water filters remove viruses?

The CDC says most portable water filters remove parasites but not viruses or bacteria. A filter needs an absolute pore size of 0.3 micron or smaller to also remove bacteria. Virus removal is where a purifier differs from a filter.

The EPA guide standard sets the bar for a water purifier. It asks for at least 99.9999% of bacteria, 99.99% of viruses and 99.9% of Cryptosporidium or Giardia cysts. The EPA does not test these claims itself.

Sawyer's own figures for the Squeeze are 99.99999% of bacteria, 99.9999% of protozoa and 100% of microplastics. Viruses do not appear in that list. The filter is a 0.1 micron absolute hollow fiber and ships with a backflush syringe. Freezing voids the filter warranty according to the maker.

LifeStraw Personal states 99.999999% of bacteria and 99.999% of parasites at 0.2 micron. Its specification says plainly that it does not remove viruses or chemicals. The maker says it meets US EPA NSF P231 for bacteria and parasites.

The GeoPress figures match the levels in the EPA guide standard for a purifier. The maker states 350 cycles or 3 years of cartridge life. Aquatabs are US EPA registered in all 50 states according to the maker. Outdoor Life puts the treat time at about 30 minutes.

• GRAYL GeoPress 24 oz: a press purifier bottle claiming 99.99% of viruses, 99.9999% of bacteria and 99.9% of protozoan cysts
• Aquatabs: NaDCC chlorine tablets with a maker's claim of 99.99% of viruses plus bacteria and Giardia cysts
• Boiling: the CDC says a rolling boil for 1 minute kills germs and advises 3 minutes above 6,500 feet

Stored water comes first since Ready.gov advises one gallon per person per day for several days. A filter or purifier is the backup for when that runs out. A purifier with a virus claim or chlorine tablets cover the gap that a plain filter leaves. Filter life and capacity figures are claims by the maker.