Arjen Hoekstra developed the idea recently, which tracks how much water people use and how much water is used to create the foods and products they consume.
"His equation is actually just a couple of numbers used to describe the amount of water that is used -- or polluted -- during the manufacture of various products. Anyone can calculate their water footprint by looking at the amount of water they use directly and then by looking at the amount of "virtual water" they use -- that is, how much water is used in the production of any goods they consume. The global average for an individual's water footprint is 1,243 cubic meters of water per year. In the US, this goes up to 2,483 cubic meters per year; in Germany it's 1,545 and in China, 702."