What’s the most cost- and weight-effective way to treat water while backpacking?

I can’t say I’ve used the Aquamira Frontier ($10; aquamira.com) yet, but it’s certainly worth a look. The device is simplicity itself—basically, a straw with a filter attached. Unfurl the straw, stick it into a water bottle, and sip. The unit is billed as capable of removing nearly all giardia, cryptosporidium, and other nasties. It’s not a purifier—viruses and very small bacteria can get through—but you could use it in conjunction with something such as MSR Sweetwater Purifier ($10; msrgear.com) for nearly total protection from water-borne badies.

Drawbacks? Well, yes. Even Aquamira bills it as more of an “emergency" filter, or as a backup to a larger filtering unit such as a Katadyn Pocket Filter ($229; katadyn.com). It also is limited to about 20 gallons of filtering. Enough for one person for a week, certainly. The other drawback with gadgets like this is that they tend to force you to “sip," rather than “drink."

My own preference is the MSR Miniworks EX ($85) which I find to be effective, sturdy, and easy to use. It does weigh nearly a pound, so that’s an issue. But it can filter a lot of water in a fairly short period of time.

The 2008 Winter Outside Buyer’s Guide is now online. From snow sports to trail-running to camping, get reviews of more than 300 new gear must-haves.