This is the most crucial distinction to understand. Think of water purification as a multi-stage journey.

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  RO Water (Pure Water): This is the result of the first major hurdle. Reverse Osmosis uses high pressure to force water through a semi-permeable membrane, removing over 95-99% of ionic contaminants, large particles, and organics. It's excellent for general lab tasks like glassware washing, buffer preparation, and feeding autoclaves. However, it still contains small ions, gases, and fine particles.

  
  


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  Ultrapure Water (Type 1): This is the final, polished product. UPW is produced by passing already-purified RO (or DI) water through additional stages, typically a mix of technologies like:

  
  
  
  
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    Ion Exchange: Removes the remaining ionized impurities.

    
    
  
  
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    Activated Carbon: Eliminates organic compounds and chlorine.

    
    
  
  
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    UV Irradiation: Sterilizes microorganisms and oxidizes residual organics.

    
    
  
  
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    Final Filtration: A 0.2 µm or 0.1 µm filter removes any remaining particles and bacteria.

    
    
  
  
  
  

In short, RO water is pure, but Ultrapure Water is reactive-grade pure. Its resistivity is 18.2 MΩ·cm, and it has virtually no contaminants that could interfere with the most sensitive analytical techniques.

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