One of our favorite wilderness essentials, the Steripen Classic 3 Handheld Water Purifier with Prefilter Bundle Pack uses shortwave ultraviolet light to disinfect our backcountry drinking water. The Steripen system disrupts the DNA of harmful bacteria, viruses, and protozoa so they won't infect us on our adventure or afterward. The Prefilter screws onto 63mm-thread bottles, creating a tight seal that removes particles and debris from the water.