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    Question ID:   12793         Current Version: 1
Question: How do water filters work?
Category: Food & Drink > Non-Alcoholic Drinks
Keywords: hole, size, work, drinking, water, filter, filtration
Type: how
Rating:(0 ratings)    Views: 235    Discussions: 0   In Watch Lists: 1  

 
    Answer:

A water filter is composed of a screen with many microscopic holes. The smaller the holes, the more contaminants the filter can remove. Filter holes are measured in microns. (The period at the end of this sentence is 500 microns.) When considering filter size, look for an absolute (the largest hole), not a nominal (the average hole), rating. EPA and CDC recommend an absolute one micron filter (or one labeled for cyst removal) to remove Cryptosporidium.

Some contaminants and their size in microns:

  • Giardia lamblia - 8 to 12 microns
  • Cryptosporidium parvum - 4 to 6 microns
  • Bacteria (such as E. coli and salmonella) - 0.2 to 4 microns
  • Viruses - 0.004 to 0.1 microns (Generally, only a few filters, such as ultrafilters and reverse osmosis, have holes small enough to assure removal of all viruses. However, viruses can be killed using a disinfectant).

Source: EPA

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