the world is not only hungry,but also thirsty for water. this may seem strange to you, since nearly 75 % of the earth's surface is covered with water. but about 97% of this huge amount is sea water, or salt water. man can only drink and use the other 3% -- the fresh water that comes from rivers, lakes,underground, and other sources. and we cannot even use all of that, because some of it is in the form of icebergs and glaciers. even worse, some of it has been polluted.
however, as things stand today, this small amount of fresh water, which is constantly being replaced by rainfall, is still enough for us. but our need for water is increasing rapidly-- almost day by day. only if we take steps to deal with this problem now can we avoid a severe worldwide water shortage later on. a limited water supply would have a bad effect on agriculture and industry. let me give you just one small exampie of how necessary water is to industry. did you know that to produce a single ton of steel, it takes about 91, 000 liters of water?
we all have to learn how to stop wasting our precious water. one of the first steps we should take is to develop ways of reusing it. experiments have already been done in this field, but only on a small scale. for us, the systems are as important as the spacecraft.
節約用水
我們的世界不僅饑餓，而且因為缺水而干渴。對你來說這可能似乎奇怪：因為我們的地球表面75％由水覆蓋著。但是，這巨大的數量中97％是海水、或咸水。只有剩下3％
的來自河流、湖泊、地下，和其他來源的淡水供人們飲用、使用。即使如此，這3％的水源我們也不能夠完全使用，因為有些淡水是以冰山或冰河的形式存在。更糟糕的是，一些水源已遭受了污染。
然而，盡管按現狀看來，這些少量的淡水即使時常轉化成雨水的形式，對我們來說，也仍然夠用。可是我們對水的需求卻日益迅速增長。我們只有現在采取措施解決這一問
題才能避免未來世界范圍內的嚴重水資源缺乏。限量供水會對農業和工業產生不良的影響。我們舉個小小的事例就能證明水對工業的必要性。每生產一噸鋼材就要消耗91，000升水，你知道嗎?
我們必須杜絕對寶貴水資源的浪費。我們應該采取的第一步就是要發展水再利用的方法。該領域的實驗已在進行，但是僅是小規模地進行。水資源再利用系統的重要性
對我們而言，與空間站不相上下。
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