For what it's worth, I differ with Chris's design above (and the first few sand filters made were more or less like what he describes). It's basically the reverse of how you want to do it: big rocks or urbanite for the bottom layer where the perforated pipe (and no cloth) resides, then smaller rocks above that, then coarse sand, and finally fine sand.
Dale Hodgins wrote:I doubt that there would be much UV pathogen killing going on. But, almost everyone can come up with a big glass jar. After the water runs through filtration and is gathered, I wonder if it could simply be bottled and placed in the Sun for a day or two. This might require the acquisition of a few jars. Sunlight is a great sterilizer , and that part of the world has no shortage. The water would also undergo a very large temperature swing, during those couple days of sterilization.