Industry, too, needs water. It takes about 22% of the world's withdrawals. Domestic activities take the other 8%. Together, the demands of these two categories quadrupled in the second half of the 20th century, growing twice as fast as those of farming.
工业同样需要用水。工业用水约占世界总用水量的22%。家庭用水占另外的8%。这两种用水加起来的总量在20世纪后半叶翻了两番,其增长速度是农业用水增长速度的两倍。
Meeting that demand is a difficult task. One reason is that the supply of water is finite. The world will have no more of it in 2025 or 2050 than it has today, or when it lapped at the sides of Noah's Ark. This is because the law of conservation of mass says, broadly, that however you use it, you cannot destroy the stuff. Neither can you readily make it. If some of it seems to come from the skies, that is because it has evaporated from the Earth's surface, condensed and returned.
满足上述的用水需求是个艰巨的任务。原因之一是水的总董是有限的。无论是到2025年还是到2050年,地球上的水不会比今天的水多,也不会比当年轻拍诺亚方舟船舷的水多。这是因为根据质量守恒定律,大体上而言,无论怎么用,你都消灭不了水这一物质。当然你也不容易制造出这一物质。如果说一部分水好像来自天空,那是因为它从地球表面蒸发、浓缩、又重新降落到地球表面的缘故。
Most of this surface is sea, and the water below it—over 97% of the total on Earth—is salty. In principle, the salt can be removed to increase the supply of fresh water, but at present desalination is expensive and uses lots of energy.
地球的表面大部分是海洋,海洋里的水——占总量的97%以上——是咸的。理论上,可以除掉海水中的盐分,以增加淡水供应量,但目前海水淡化既昂贵又需要消耗大量能源。
来源:可可英语 http://www.kekenet.com/daxue/201810/566582.shtml