This compact purifier is a must-have for any hiker or traveler who wants to keep bulk down. The CrazyCap uses UV rays to eliminate viruses, bacteria, and protozoa; just screw it on to the included stainless-steel bottle, press the “on” button, and wait as it disinfects your water. Two modes run the purifier for either one or two minutes, depending on water quality (you will need to prefilter silty water, though). The cap fits most 17-ounce disposable bottles and their reusable equivalents, although it’s too small for large-mouthed vessels, like a Nalgene. The device’s charge holds for seven days at four uses per day in one-minute mode. Bonus: The CrazyCap turns on for 20 seconds every four hours to disinfect the bottle itself and zap any stragglers.