Because of the importance of pure water for good health, the act of boiling water is an essential task in many parts of the world. History tells us that Emperor Shen Nung was one of the first people to discover the importance of boiled water, as well as having discovered tea. Today, the consumption of tea is just as important as the consumption of drinking water. On average about 2½ million metric tons of tea are produced worldwide. Some of this tea is retained by producing countries for internal consumption, while the rest is traded either directly to value-added resellers in other countries or bought through auction on the open market. India and China are the largest consumers of tea on the basis of total leaf used, and this consumption is largely from internal production. These countries are the largest producers of tea, as well. The UK is the largest per-capita consumer of tea averaging about 3.5 to 4.0 cups per day.