The LifeStraw Flex with Gravity Bag is a water filter system that protects against 99.999999% of bacteria (including E.coli, Salmonella), 99.999% of parasites (including Giardia and Cryptosporidium), 99.999% of microplastics, chlorine, organic chemical matter, dirt, and, and cloudiness; and improves taste in the process! This versatile water filter system can be used 4 ways: As a personal straw filter