Disclaimer. This water filter will not make the water SAFE. It will only render it clear and make it more palatable. you must boil it afterwards or use another form of proper disinfection. SODIS or Solar Disinfection would work.
In this video I go through the processes of constructing a primitive filter utilizing natural recourses such as charcoal from a fire, moss, and sand. I use a soda bottle as the filter container to show you the individual layers and to see the water seep through the layers.