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Help with reverse osmosis

  1. May 28, 2012 #1
    HI, this is the first time I have posted on this site.

    I know very little about physics, so am not sure if this is ok to post here, but I wondered if anyone could tell me if reverse osmosis is a true phenomena and whether reverse osmosis water filters (which you can buy and fit to your taps at home) actually work? If so do you know exactly what it filters out? I presume heavy metals and things which are suppposed to be bad for us? What about minerals and the good things that are in water?

    Many thanks

  2. jcsd
  3. May 28, 2012 #2
    Reverse osmosis takes place at a pressure greater than osmotic pressure. A SPM(semi-permeable membrane) is required.
    What gets pass the membrane gets filtered out of the water and this depends on the nature of the SPM. That is, different materials used as SPM allows different substances to pass and block others. Therefore, in water purifiers, the SPM is taken that only filters inpurities and not useful substances
  4. May 28, 2012 #3
    Thank you for your quick reply!

    So does that mean that that the molecules for the bad stuff are bigger than that of minerals and good stuff and therefore cannot pass through? Otherwise how does the SPM differentiate between the two groups?
  5. May 28, 2012 #4


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    Yes. It's just a very fine strainer working under quite high pressure.
  6. May 28, 2012 #5
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