Here is a detailed and extensive discussion of the merits and negatives of various water treatment techniques: https://en.wikipedia.org/wiki/Portable_water_purification

Lots of options out there and none are clearly superior in all circumstances. I note that chlorine will require at least thirty minutes or more in order to become fully effective and is not necessarily fully effective against Clostridium (sp?) or Guardia.

When it comes right down to it, I will drink unfiltered water so that I can get back to town. Once there, I can seek cures for whatever ailment I might have acquired. I did this routinely some years ago, usually from springs and seeps in unpopulated areas. I have never suffered any bad consequences from this practice, although now I am considerably more cautious than I was in the past.....