This is the FILTERPEN, a personal water filter that can convert non-drinking, and contaminated water instantly to fresh drinking water . Ideal for camping, hiking, and a great companion if faced with emergency conditions. It's lightweight and compact, so it's an easy addition to your go-bag or your camping backpack. The filter can be used for up to 264 gallons of water. It's really easy to use--just put the lower part of the straw into whatever water you would like to drink and sip. The water will be filtered by the time it reaches your tongue. We recommend the FILTERPEN as an addition to any emergency preparedness kit, camping bag or adventure pack.