I would think that most of us, if we have to purify any significant amount of water, will use the simplest, most effective method of all - boiling.<br><br>I always have some sort of container with me on trips of any length that can serve for that purpose (Altoids tins are a bit small).<br><br>Of course we go into considerable detail about the containers, etc for other possible techniques, but look at the detail we lavish on those sharpened slivers of steel that we regard as essential equipment. That is the joy and strength of this list.