Water-borne, diarrhoea-causing bacteria, such as E. coli, kill 1.6 million people every year.
Those filters are made from clay because it's easy to use and most importantly... it's free.
But fired clay alone is too dense to let the water pass at a desirable pace. Therefore some organic material is being added to increase the porousity: Organic material - like used coffee grounds, grounded rice husk, tea leaves or straw, papier-maché... - will would burn up in the firing process and leave tiny holes in the clay.
Clay and Grounded coffee are materials widely available around the world.
Mix equal parts: One handful of clay, one handful of coffee grounds, for exemple from a collecting bin at the local coffee shop. Mix with enough water to form a thick biscuit like paste and form a cylindrical recipient with this paste. The walls of the filter should be as thick as an adult's index.
Leave it in the sun to dry.
fire the clay with cow manure: pack the pots in dry straw, and after you lay them on a first layer of dry cow dung, cover them with it completely.
A dung fire burns at around 950 degrees C - the right temperature for firing clay. The filters should turn bright orange during the firing process and stay so for 30 min.
It normally takes about an hour of baking in the dung to fire the filter.
The bacteria are slightly bigger than the pores of clay and get trapped in the clay. The coffee increases the porosity and the contact surface of the clay.
Lab tests showed that the clay and coffee combination works well: it takes one to two hours to filter one litre of water, and the coffee-clay filter removes up to 99.8 percent of bacteria in water.
This page was last edited on 30 January 2014, at 11:50.