How small would the holes have to be in a sieve for dirty water to be purified if at all possible?

Question: How small would the holes have to be in a sieve for dirty water to be purified if at all possible?
- Keywords:
- Royal Society of Chemistry: Find out more on:
  
  clean
  
  environment
  
  sieve
Asked by to Ben, Emily, Hattie, Jemma, Veronica on 24 Jun 2014. This question was also asked by .
- Emily Hayward answered on 24 Jun 2014:
  
  Great question muzzasif2000!
  
  It depends howpure you want it – when sieves are very small they tend to be classes as membranes……they look a bit different from the sieve you’d use in a kitchen but work in a very similar way. You can get membranes with holes in them only a couple of nanometers wide which means most molecules cant fit through, but water, and anything maller than water can get through. Most molecules are bigger than water, particularly harmful ones therefore these can be used to purify water (and are the main way water is currently purified!)
  
  Hope this helps answer your question.

Question: How small would the holes have to be in a sieve for dirty water to be purified if at all possible?