The Katadyn Guide Filter Element is a replacement element that fits the Katadyn Guide, PUR Guide and PUR Scout Purifiers. This element does not purify, it only filters. But it does an excellent job at that, using 0.3 micron screens to filter out particles, bacteria and protozoa. Make sure you fit a fresh one before you set off on your adventure. And if you're gone for longer, maybe bring a spare to make sure you've got freshly filtered water available all the time.