i use a Steri-PEN for water purification in the backcountry. i like it due to no pumping or anything of that nature. All you do is filter it with the prefilter to get the chunks out (prefilter fits on top of Nalgene) then stir the water with the wand for a minute and a half. UV rays kill everything. The whole thing is super small and lightweight. The only bad thing about it is that it uses batteries, so make sure you have a spare set just in case.

It can be viewed here:

http://www.rei.com/product/761906

Later

Rob