Unless you plan to carry enough water for your entire trip you need to have some sort of water purification system. Katadyn manufactures the two top selling water filters in the world and their design,durability and ease of use make them a joy to use. The Guide is perfect for groups and can pump one liter of water in 36 easy strokes. It features a low maintenance design - no cleaning required - and comes with 36" hoses, prefilter, universal bottle adapter and a carry bag. Guaranteed not to clog for one year. Replacement cartridge also available.