The only thing easier than this UV purifier would be to drink straight from the creek. And what climber doesn’t relish an occasional swig of glacial melt? But this device gives serious peace of mind: Ultraviolet light neutralizes all water-borne nasties. Swirl the purple light in a liter of water for 90 seconds, and the screen shows smiley (success) or sad (try again) faces. Bonus: it’s rechargeable (USB or AC/wall); you’ll get about 50 zaps on one charge.