水是自然环境的重要组成部分,是人类生产活动经常取用的自然资源,没有水,人类就不能生存。全球约有138.6亿亿立米的水,以固态、液态、气态广泛分布在地球的“水圈”中。从广义来说,地球水圈中各个环节、各种形态的水都可以称之为水资源,因为它们之间是密切联系的,对人类均有直接或间接的使用价值。狭义的水资源,是指可供人类经常取用的水量,亦即大陆上的动态水资源。大气降水是大陆上动态水资源的补给来源,它除了补给地表水和地下水外,并有一部分直接补充土壤水为植物生长所利用,这部分水量不能为人类所控制,不属于目前水资源评价的范围。故水资源量的调查和评价包括地表水资源和地下水资源。但地表水、地下水和土 Water is an important part of the natural environment and is a natural resource often used by human activities. Without water, human beings can not survive. There are about 138.6 billion cubic meters of water in the world, widely distributed in the “hydrosphere” of the earth in solid, liquid and gaseous forms. Broadly speaking, all aspects of the Earth’s hydrosphere and various forms of water can be called water resources because they are closely linked and have direct or indirect value for human use. Narrow water resources, refers to the amount of water available for human often access, that is, the dynamic water resources on the mainland. Atmospheric precipitation is a source of dynamic water resources on the mainland. In addition to replenishing surface water and groundwater, a part of it directly replenishes soil water for plant growth. This part of water can not be controlled by humans and does not belong to the current assessment of water resources range. Therefore, the survey and evaluation of water resources include surface water resources and groundwater resources. But surface water, groundwater and soil