SP191 Delivers 5 gal. of clean drinking water in under 45 min and up to 170 gallons in one day. Includes a back wash syringe and a faucet adapter for thorough back washing in the field and at home. Low cost and high volume. No Pumping, No Chemicals, No Waiting and No Worries. Easy to use. The Sawyer Point Zero Two Purifiers features a 0.02 Micron Absolute Hollow Fiber Membrane, which uses medical technology developed from kidney dialysis. When the water is drawn through the filter, it flows through the side walls of the Hollow Fiber tubes. Sediment, bacteria, protozoa, cysts, and other contaminants are filtered out, exceeding all applicable EPA recommendations. To use the Sawyer Point Zero Purifier simply follow the instructions enclosed and affix the purifier to any bucket or pail to yield bacteria-free water in remote locations. The only external force required for the system to function is gravity. The flow rate of a purifier is determined by a combination of head pressure, altituted and how clean the filter is. Absoulty no chemicals needed and is rated for One Million Gallons. Sawyer is confident in their one million gallon claim because you can continually clean the filter by backwashing it with clean water. Backwashing is not required often unless you are filtering very turbid water. Backwashing is as simple as reversing the filter flow with clean water. Forcing the clean water back through the filter flushes out all of the contaminants and only takes a few seconds. NO REPLACEMENT FILTERS OR CARTRIDGES ARE NECESSARY. We trust you will thoroughly enjoy the ease and extra protection this proven next generation technology offers you. 1 Million Gallons Guaranteed Sawyer's Guarantee: The Sawyer Company is confident in their million gallon claim because you can continually clean the filter by backwashing it with clean water. So there really is no end to its useful life. That is why they can GUARANTEE THE FILTER FOR LIFE as long as you follow the simple care and use instructions. Follow the helpful hints included in the directions for use. Backwashing is not required often unless you are filtering very turbid water. Backwashing only takes a few seconds. If you are accustomed to a ceramic filter, the leaning ratio is approximately 20:1. In other words, by the time you first need to clean your hollow-fiber filter you would have needed to clean a ceramic filter 20 times. NO REPLACEMENT FILTERS OR CARTRIDGES ARE NECESSARY.