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The world is not only hungry, it will also be thirsty for water. About 97% of water on the earth is sea water, or salt water. Man can only drink or use the other 3％迹唤of the fresh water （淡罩哗水）which comes from rivers, lakes and underground. On the other hand, because the number of people in the world is becoming larger and larger, more and more fresh water is needed. So water shortage becomes a big problem.
How can we work out this problem? Scientists have found some ways to turn salt water into fresh water. One important way is to boil （使达到沸点）sea water with high heat until vapor （蒸汽）物州行rises, leaving the salt. In this way, a lot of fresh water can be made quickly.
But heating is not the only way to get fresh water. Other ways are tried, for example, digging deep wells, keeping rain water and preventing rivers from being polluted.
http://www.5ykj.com/Health/jiu/33782.htm