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I know that water boils at $100~^{\circ}\rm C$. I also know that the standard way to purify water is to boil it for roughly a minute. What I'm curious about is, what properties of the boiling process purify the water?

Is it purely a temperature thing? Are we saying "roughly a minute" so that the temperature actually increases beyond $100~^{\circ}\rm C$, thus reaching some actual temperature needed to kill bacterial/viral stuff? Or, does the "rolling" of the boil actually add a physical benefit to the purification process?

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    – M.A.R.
    Nov 10, 2015 at 21:22
  • $\begingroup$ Unless you're adding a lot of salt to your water, you're not going to get a temperature above 100 ºC. In fact, at high altitudes (e.g. backpacking) your boiling water will be at lower temperature than 100 ºC. $\endgroup$
    – S. Burt
    Nov 10, 2015 at 21:33
  • $\begingroup$ @S.Burt - very intriguing! Care to explain why this is, or is that fit for another question? $\endgroup$
    – MrDuk
    Nov 10, 2015 at 21:35
  • $\begingroup$ I suspect there are several questions related to boiling point change already here on chem.SE. In short, the boiling point of any pure liquid depends only on the external pressure (hence, higher altitudes have lower boiling liquids). You cannot exceed the boiling point by adding more heat or waiting for more time. This boiling point can be change, however, by dissolving other things into the water (try searching for colligative properties for an explanation). $\endgroup$
    – S. Burt
    Nov 10, 2015 at 22:30

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There nothing special about boiling that is doing anything. For example, you can put a beaker of water under vacuum and get the water to boil at room temperature, but that won't kill any bacteria or render any viruses impotent.

It's purely a heat thing. You want to destroy any pathogens that may cause illness. Sufficient heat will denature proteins in a virus and kill bacteria, etc. Boiling simply gives you a visual cue that you've reached a very high temperature (so you don't need a thermometer) and the ~1 minute is just to ensure that you sustain a high temperature long enough to destroy any bacteria or viruses.

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    $\begingroup$ An additional point of boiling via heating is that it creates convection currents which stir the water well. // I attached a link to a nice chart which has time/temperature needed to kill some certain organisms. cid.oxfordjournals.org/content/34/3/355/F2.large.jpg $\endgroup$
    – MaxW
    Nov 10, 2015 at 22:12
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    $\begingroup$ Fantastic reference. Some of those temperatures were lower than I would have expected, but I was surprised that hepatitis can survive up to 98 ºC. $\endgroup$
    – S. Burt
    Nov 10, 2015 at 22:24
  • $\begingroup$ I should have pointed out that boiling is an absolute guarantee. Some bacteria have spore forms which are not killed by boiling. $\endgroup$
    – MaxW
    Nov 10, 2015 at 22:27

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