Backpacjac,

Filtration is probably the best for most of North America. I use an old Katadyn pocket filter the most. Crypto is a common problem, virus much, much less so. Some of the new Sawyer filters appear to remove the virus component also. Overseas you are going to need both. None of the chlorine based products will.touch crypto. Chlorine Dioxide (and the miox from MSR) will do it, but only with extended contact time (four hours is common). The Steripen is nice, I have and use one, but it has limits too. The biggest problem is cross contamination, particularly if you use their recommended procedures. It also only does one liter at a time, not much if you want a meal for a group, or to clean up. In canoe country, working from a base camp, I use the MIOX for a large bladder at camp (fill before leaving/bed) and the Steripen for drinking water in the field.

Respectfully,

Jerry

P.s. Boiling is best, I use it in preference to the others when it is practical. The Wilderness Medical Society recommendations (from lots of experimental data) is only to a rolling boil.