The two-liter bottle filter.

1. 1

   What you need

   
   • A clean two-liter bottle and a knife
   • Coffee filter or clean cloth
   • Gravel, coarse sand, fine sand, charcoal
2. 2

   Cut the bottle

   
   • Take the bottom third off
   • Keep the cap, poke a few small holes in it
   • The neck end is the outlet, pointing down
3. 3

   Cloth first, at the neck

   
   • Push the filter or cloth into the neck
   • This stops the layers washing out
   • Pack it snug, not tight
4. 4

   Charcoal layer

   
   • Crushed charcoal from a cold fire, or activated charcoal
   • Rinse it first until the water runs clear
   • Two to three inches deep
5. 5

   Fine sand

   
   • Two to three inches on top of the charcoal
   • Catches fine sediment
   • Rinse it before it goes in
6. 6

   Coarse sand

   
   • Another two to three inches
   • Catches the mid-size grit
   • Keeps the fine sand from clogging
7. 7

   Gravel on top

   
   • The last inch or two, biggest pieces
   • Breaks the pour so the layers stay put
   • Clean gravel, not garden dirt
8. 8

   Pour slow

   
   • Trickle the water in, do not dump it
   • The first batch comes out dark, discard it
   • Keep going until it runs clear
9. 9

   Collect it clean

   
   • A clean jar under the neck
   • Cover it while you wait
   • Expect it to take a while
10. 10

    Now make it safe

    
    • Boil one minute at a rolling boil
    • Or 8 drops of unscented 6% bleach per gallon, wait 30 minutes
    • This step is not optional
11. 11

    What it will never do

    
    • It does not remove germs
    • It does not remove chemicals or salt
    • Clear water can still make you sick
12. 12

    Rebuild it, do not reuse it

    
    • The layers hold what they caught
    • A new filter for each day of use
    • Keep extra sand and charcoal dry

This clears water. It does not make it safe. Boil it or bleach it after.