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水是自然界的基本要素,是一切生物赖以生存的基本条件之一。随着人类社会经济的发展和人口的增长,特別是近代社会生产力的巨大发展,人类对水的需要数量日增,不少地区出现了水资源的紧张局面。人们开始认识到,水资源并不象以往所想的那样是取之不尽、用之不竭了。地球表面和地壳中的水确有不少。地球表面约有70％为海洋水所复盖,而其余占30％的陆面及其地下也都有水的存在,水同时存在于遍布陆地和海洋的一切生物体中,在整个包围着地壳的大气层中也都有水汽或水
Water is an essential element of nature and one of the basic conditions for all living things to survive. With the development of human society and economy and population growth, especially the great development of social productive forces in modern times, the human need for water has been increasing day by day. In many areas, there has been a tense situation of water resources. People began to realize that water resources are not inexhaustible, as they used to be. There is quite a lot of water in the Earth’s surface and in the earth’s crust. About 70% of the Earth’s surface is covered by ocean water, while the remaining 30% of the land surface and its subsurface also have water present in all living organisms throughout the land and sea, The atmosphere also has water vapor or water