I haven't been in a situation where I needed extra water yet, but last month I got a good deal on an MSR Miniworks EX filter... I guess i'm going to take it with me on many future adventures. Especially if I know that there are lakes/streams where I could use it.
Good pick. MSR makes really good filters. You can even get viral protectionwith some models, and as add-on with others. I think the Miniworks is an add-on for viral protection.