For more reading on water purifying you might want to check the archives at Swamp Rat Survival Forum. You might try doing a subject only search in the survival forum using the search term "water" for more discussions on it.
I read a paper not to long about the chances of getting sick from wilderness water. I wish I could find the article. Anyway the gist of the paper was that you really had very little chance of getting sick from untreated water provided that it's flowing in some capacity. And that the issue of viruses and bacteria was largely blown out of porportion. However, given that information I think I'll continue to treat my water as long as it's practical and possible to do so. It really cannot hurt.
I sorta agree with you Jerrwhy as to the possibility of a lot of hype(lots of money in water treatment) but I was once very sick. Doctor figures it was either Ecoli or Giardeha(sp?). Either way I was puking and crapping violently literally at the same time. This was not a case of the runs that would be merely uncomfortable or a bother. This was I can't move from dehydration and pain. If I was in the woods without help I am certain that it would have taken luck or will to survive it. Doctor had asked me why I didn't come to the hospital at the time and I really could not move and as long as my wife was getting me water, I liked my home better than a hospital. I always treat water just in case <img src="/ubbthreads/images/graemlins/smile.gif" alt="" /> I have been told that once a person has giardea and gets through it with out meds, the body is immune to it but I am not taking chances.
Life is a grindstone. Whether it grinds you down or polishes you, depends on what you're made of
you can boil that way in paper, a leaf, just about anything, just use the heat not the flames, and a one time thing. Foil would be easy to carry in your psk or in your pocket.
