Designs: a Water-Purifying Straw, a Firewood-Saving Cookstove

The LifeStraw is a thick plastic tube twenty-five centimeters long.  You place one end into water and drink from the other.  The water passes through a series of filters to catch extremely small particles.  Iodine and active carbon are also used in the cleaning process.  It all takes about eight minutes for one liter.