• Question: hi Richard, i was just wondering do you know how many Bactria cells you usually have to kill do get pure water? and how long do you estimate it takes to get pure water? thank please get back.

    Asked by JACK DA KING to Richard on 19 Mar 2015.
    • Photo: Richard Simons

      Richard Simons answered on 19 Mar 2015:


      Since it’s actually quite hard to count bacteria outside of the lab we conduct standardised studies to test effectiveness. In the lab we’ll create a sample with a known number of bacteria – measured in colony forming units per millilitre (CFU/ml) – this number is typically very large, for example 10^6 (1 000 000) CFU/ml.
      We then treat the sample, and measure the live concentration afterwards. What we’re looking for is the reduction – end/start; so if we start with 10^6 and end with 10^2, we have a reduction of 10^4, meaning that 99.99% percent of the bacteria have been killed.

      If we know that 99.99% of bacteria in our reference sample have been killed, then we know that 99.99% of bacteria in a ‘real world’ sample would also be killed, so we know that our treatment is working.

      Apologies for the complex answer, it’s quite a maths-heavy concept.

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