LifeStraw Mission Water Purification System, High-Volume Gravity-Fed Purifier for Camping and Emergency Preparedness Gravity-fed, high-capacity, hollow membrane water purifier; ideal for group and family camping, outdoor activities, and emergency preparedness Removes virtually all bacteria (99.9999%), protozoa (99.99%), and viruses (99.999%) that can contaminate water; easily fillable in lakes and streams Compact roll-bag reservoir available in 5-liter (1.3 gallon) or 12-liter (3.1 gallon) size; can be suspended from tree or other support for easy access Simple to use and maintain, without chemicals, batteries, or moving parts; features carrying strap and includes stuff sack for storage and portability Lifetime filtration capacity of 18,000 liters (4,755 gallons); produces flow-rate of 9-12 liters (2.4-3.4 gallons) of purified water per hour