With shows like "The Walking Dead" and others, students are interested in how to survive the Zombie Apocalypse. One thing they will need is an improvised water filter to clean dirty water. This type of water filter was seen in a episode of "The Walking Dead". It's also featured in survival shows. You will need plastic water bottles, sand, gravel, coffee filters, marbles, and any other medium you think can be used to filter water. I do NOT recommend using charcoal or ash, because when wet they ar