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Tuesday 25 January 2005

Low cost, low tech water filtration

Aid workers in the field will find this useful.

New filter promises clean water for millions

The production of the filters is extremely simple. Take a handful of dry, crushed clay, mix it with a handful of organic material, such as used tea leaves, coffee grounds or rice hulls, add enough water to make a stiff biscuit-like mixture and form a cylindrical pot that has one end closed. Dry the pot in the sun, then surround them with straw, place in a mound of cow manure, light the straw and then top up the burning manure as required. In less than an hour the filters are finished.


The filtration process is simple, but effective. The basic principle is that there are passages through the filter that are wide enough for water droplets to pass through, but too narrow for pathogens.

Organic materials which are combined with the clay burn away during the firing process, leaving cavities that help produce the structure in which pathogens will become trapped.


Tests with the deadly E-coli bacterium have seen the filters remove 96.4 to 99.8 per cent of the pathogen — well within safe levels. Using only one filter, a litre of clean water can be produced in just two hours.
Read the full article at Australian National University
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