Zaps the viruses, bacteria and protozoa responsible for everything from diarrhea to salmonella to typhoid—just press a button, then stir in up to a liter of water while the UV light does its thing. Little (6.1 inches), light (under 4 ounces) and fast (takes 90 seconds, max). Easy to use anywhere, on water from a developing country well, a back-country stream or even a sketchy city tap.

* Solar charging case sold separately.