As known to all, the whole living world cannot survive without water becasue it is indispensable for all living things to keep themselves alive. It is irresistable law of nature that they must consume water regularly to meet their needs for existence. As early as the ancient times, man regarded water as a vital element of live.

According to scientists, nearly three fourths of our body-weight is constituted by water. We have to take in large quantities of water every day to replenish those lost through excretion and prespiration. If one is short of water, one will soon die of thirst, as are all other living things. In man’s daily life, in addition to keeping themselves alive, water has lots of purposes, such as for washing, cleaning and so on.