1 Have at least 2 containers for water. One should be used to hold unfiltered water and the other should only be used for filtered water. If you have more, one can be converted into a filter.
2Poke small holes into the bottom of the filter container. These holes should allow the filtered water through, but not the filtering materials.
3Locate filtering agents. These materials can vary in a survival situation, but good materials include small rocks or gravel, charcoal, sand, grass or cotton clothing.
It can also be useful to carry coffee filters or cotton balls in your gear.
4 Crush charcoal pieces from your campfire with a tool or rock until they become very small pieces.
5 Layer your materials to sift out different particles. You should arrange your layers to filter larger pieces out first, then increasingly smaller ones.
An example of a properly layered filter would be gravel or rocks first, followed by sand and charcoal layers and finished with cotton or coffee filters to catch the smallest particles.
6 Pour the unfiltered water into the makeshift filter and allow the water to drain into the next container. You might want to pour the water through a couple of times.