A: I like MSR's MiniWorks EX ($80, www.msrcorp.com). I've been using one for years and have found it supremely user-friendly and effective—at least, I haven't contracted giardia while using one! The two features I particularly like are the lever-type pump handle, which I find easy to use, and the fact the filter can be screwed directly onto a Nalgene bottle, so there's no need to try to balance a bottle or pot on a rock and hold an outlet tube over it. The EX is an updated version of the MiniWorks I've long used, with a new filter element and improved pumping action.

The SweetWater Microfilter ($59) is also a can't-miss filter. Like the MiniWorks, it's now made by MSR (which purchased SweetWater a few years back) so it has the same basic filter, just a slightly different design. It's being marketed as the "light and fast" filter, while the MiniWorks is for someone who's willing to carry a few more ounces and gain some durability.

Neither the MiniWorks nor the Microfilter is a water purifier, however. That means they'll catch giardiasis, protozoa, and that sort of thing, but not viruses. For that you'll need to carry along a chemical treatment. SweetWater Purifier ($9 a bottle) does the trick, without adding any aftertaste.

Everything you need to know about pumps, filters, and chemical purifiers in Outside's 2004 Buyer's Guide .