But for the others, let’s elaborate and describe the process.
1) Make the clay mixture
Crush reddish-brown terra cotta clay into a powder. Mix one handful of clay with one handful of dry, organic material (preferably coffee grounds, rice hulls, or tea leaves). Add water until the mixture is firm enough to be handled and shaped.
2) Shape into pots
Shape the clay into a cylindrical pot with an opening of about 4 inches in diameter. The wall of the pot should be as thick as your finger. Let the pots sun dry.
3) Build the fire
After the pots have sun dried for at least 6 hours, create piles of dry cow manure and place the pots on top of them. Surround the pots with straw or leaves and add two to three more layers of manure. The pots should be completely covered. Light the straw or leaves and stoke the fire until it burns steadily.
4) Add manure to the fire
The fire will reach approximately 1292 degrees fahrenheit in 30 minutes, and will reach 1652-1742 degrees fahrenheit after 50-60 minutes. (THIS WILL MELT MARAGING STEEL!) Add more manure, covering any holes in the mound, to keep the fire hot. The fire should burn a bright orange to yellow color. The filters should fire at that color for at least thirty minutes.
5) Remove the pots from the fire
After 45-50 minutes the organic material will burn away and the pots can be removed. They will be red hot, so do not touch them. More pots can be put on the fire at this time, if you have them, and covered with additional manure.
6) Filter water
Allow the filter to cool. Rinse out any charcoal or dirt and fill with water. After the first round of water is discarded, filters are safe and ready to use. The filters can be held or set atop bottles or glasses to catch the clean water during the filtration process.
These are going to filter very slowly. SOOO.. Go nuts – make a bunch and when you need to filter water you’ll have more, faster.