一、水资源的有限性 根据自然资源的不同特点,人们通常将自然资源划分为三大类,即生物资源(可更新资源)、矿物资源(不可更新资源)和生态资源(恒定资源)。太阳辐射、热量、水分、风能、海潮等属于生态资源,这类资源具有显著的区域性特点,合理开发它们,发挥各地所长,可以永恒使用,即人们常说的是“取之不尽、用之不竭”的资源。 水资源作为恒定资源之一,是由于水资源被开发利用后,并不导致它们在地球上的总储量减少。应该指出,对水资源来说,总储量的不变,只能是从全球的宏观角度出发,这里所说的水资源是广义的概念。广义地来说,海洋、地下水、冰川、湖泊、土壤水、河川径流、沼

Recently, the fresh water resource is facing a crisis which is becoming increasingly acute day by day in most countries as well as in China. The contradiction of water supply-demand is the reflection of relationship between water supply and water demand, affected by water quantity, water quality, distribution pattern and exploitation condition, and closely related to the water resource demands of various departments. The contradiction is the result of comprehensive influence affected by a number of natural and economic factors. As we know, the water in nature is limited, and the distributions of water in different place and times are extremely uneven. With the increase of consumption, water resource has become insufficient in many regions. In China the actual total fresh water consumption reached about 470 billion m3 by the end of the 1970's, around 4.7 times the amount of consumption of the years just following the liberation. In cities living consumption of water has been multiplied by 8 times while that of industry (including thermal power) by 22 times. In some regions and cities, the amount of water consumption has already reached the available point of moderate water year. In the slight low water year the supply does not match the demand. And in the very low water year the problem of scanty fresh water would become really serious.From the point view of tapping new sources of water, desalination of sea water should be developed in regions and cities near the sea. But the cost is much high now. For most cities far from the sea, the sea water is unavailable. By way of the water transported across watershed, the water resource can be redistributed among the districts. Of course, this is the one method worth to be paid attention to. But to do so is much complicated; the con is so expensive that it is difficult to practise in very short period. In many regions and cities water supply insufficient, while tremendous waste of water is really existing. And to reduce consumption is a potentiality in daily life and production. So the basic means to mitigate the contradiction between supply and demand of water resources is to reduce consumption. On the basis of overall reducing consumption, vigorous measures should be adopted to tap new sources and to get a reasonable management of water resource.