Almost everyone knows that water covers three-fourths of the earth's surface. Most of it， however， is in the oceans and is too salty to drink. Also， some of it is frozen and cannot be used. In fact， less than one percent is left for the use of people， animals and plant life. All through history men have tried to build their homes near the sources of fresh water. Now fresh water is becoming scarce， but more and more is needed because of the increasing number of people in the world. Some industries also use large amounts of fresh water in the production of things such as steel， petroleum， paper and rubber and so on. Scientists estimate that the need for fresh water will have doubled by the year 2023. If they are correct， we must find new ways of saving it or producing it. Some nations have worked on the problem and are already sharing their information with others. They are trying to keep their rivers from becoming polluted. Deep wells are also being dug， and rain water is being collected in huge artificial lakes. In one way or another， they hope to provide enough water to satisfy the needs of their people.