Keep your water free of microscopic hitchhikers that make you sick.
The Platypus GravityWorks Filter Cartridge filters down to 0.2 microns and meets EPA Guide Standards for the removal of bacteria and protozoans. Pop one in the gravity line of your GravityWorks or CleanStream filter and enjoy fresh water. Measuring just about six inches in length and a few inches wide one of these spare filters takes up minimal room in your backpacking kit. It can't hurt to keep a spare around for particularly dirty water, or large groups that require a constant supply of high quality H20.