With one 5 liter bag of chlorine, and a device that costs $3 to build, you can clean 100,000 liters of water.
Here at Maker Faire Africa is Killian Deku, a Ghanaian working in the IDDS program, has created a ball valve chlorine doser with the help of his team mates from India, the US and Tanzania. Their only real costs were the ball valve and the time taken to create the bamboo structure that holds it. The one variable cost is the bag of chlorine used to cleanse the water.
Ball Valve Chlorine Water Cleanser from WhiteAfrican on Vimeo.