4.2 Water Filtration
Bio-sand Filter
http://www.lwdgc-africa.org/15.html
Water passes through sand and gravel layers and then comes out of the filter at a rate of 1L/minute. There is always a small amount of water that does not drain from the filter, and this standing water develops a slime on top, which forms a biological layer filled with aerobic bacteria that eat the bad bacteria. 90% of the bacteria are removed as water flows through this top biological layer, and then the sand filters out the parasites and larger organisms.
Plans available here: http://www.biosandfilter.org/biosandfilter/files/webfiles/BioSandFilter_Construction_Guidelines.pdf
HCM is developing low cost, low weight, aluminum molds that can be transported as checked baggage. Estimated cost $125. Please e-mail harvestchapelmission@yahoo.com for more information.