I use a Pur Hiker occasionally to process water, but I really prefer to boil. Simple, effective,and you get a nice cup of tea into the bargain.

The worst water I ever treated was stream water in Canyon de Chelly, where we were doing a project that required us to hike in and stay for days at a time. The water was undoubtedly contaminated. There were herds of sheep and dwellings upstream, none of which sported so much as an outhouse. The water (too thick to drink and too thin to plow) first sat overnight to settle the sediment, was decanted and boiled. Over several weeks, this worked just fine - no illness or tummy problems.

Recommendations for boiling times are all over the map. I have seen statements that as much as five minutes of a full boil are required. I seem to do fine just bringing the water to a rolling boil, and then chilling it. There have been times when I have consumed untreated water, figuring that my first priority was to make it back to town, whereupon I could deal with whatever illness might develop. As far as I know, I have never been ill from contaminated water.