This type of filter is a common solution to the problem of obtaining clean water in many parts of the world, especially rural parts of developing nations. It is a fairly simple process that involves only materials that are available in most parts of the world.
A friend of ours is away in Kenya working on various projects having to do with sustainability including filtering water for drinking. Where he is now, "water guard" tablets are used to kill bacteria, but it does nothing to improve the clarity or taste of the water so he has been experimenting with different filtering techniques. He has a local source of both clay and sawdust, making this sort of filter a viable option.
Note that this filter can only filter particles and color out of the water. It cannot filter bacteria or viruses. Water filtered through this filter is not meant for drinking, and should be boiled before being consumed.
This instructable is the culmination of a project for the Spring 2011 Stuff of History class at the Olin College of Engineering in Needham, MA.
Step 1: Raw Materials
Dry clay. Clay dust is probably easiest. (Warning! Clay dust is extremely harmful to your lungs! Only use outside, under a hood, or in another well ventilated area!)
Fine Sawdust. Best obtained by sieving sawdust. A #30 (600 Micon) size sieve works best, although other sizes can work. Smaller is not advised, as it will be a slow process to sieve and will slow the filtration rate. Larger can be used, up to the size of a window screen, although the filtration quality will suffer some.
Water. The purity of the water should not matter much.
A mold. The clay-sawdust mixture lacks plasticity, so using a mold to shape the pots is best.
Kiln/Furnace. We used an electric programmable furnace, although anything that can reach the required temperatures at a controllable rate will work.