GEF

Unit 3  |  Water Use and Human Water Systems 70 Per capita water use also varies greatly between countries. Surprisingly, there is little correlation between per capita water use and per capita income. For example, Pakistan has high per capita water use and low per capita income. Switzerland has low per capita water use and high per capita income. The U.S. has high per capita water use and high per capita income. These figures suggest that developing countries can increase standards of living without necessarily driving up water use. Defining water use is not always an easy task. Water research- ers and some government agencies differentiate between water withdrawals and water consumption . In many cases, such as using water for power plant cooling, water is withdrawn from the environment, used, and then returned to water bodies with little loss of supply. This is considered non- consumptive water use, because the water is still available for downstream users. In contrast, consumptive water use does not return the water to the environment. For example, water is consumed when it is used for agriculture, as it is not returned to the local environment or watershed after being used to grow crops. Just because water use is non-consumptive does not mean it is sustainable. Sometimes, the water may have a reduced water quality which limits its use for people or ecosystems. From a long-term perspective, the distinction between consumptive and non-consumptive water use is somewhat artificial, as all water eventually is recycled through the action of the global water cycle . The growing trend toward water efficiency is showing benefits in many developed countries. In the U.S., per capita water with- drawals peaked around 1980, and have since declined about 20 percent despite a population increase of roughly 35 percent during the same period of time. While there are several fac- tors responsible for the decline in per capita use, the important point is that current water demand is significantly lower than PER CAPITA A measure of average use per person. WATER WITHDRAWAL The removal of water from a water body for human use. WATER CONSUMPTION Water withdrawn from natu- ral sources by humans that is not immediately available following use. NON-CONSUMPTIVE Activity that does not consume or deplete the water source. CONSUMPTIVE Activity that consumes or depletes the water source. WATERSHED An area or ridge of land that separates water flowing to dif- ferent rivers, basins, or seas. WATER QUALITY The chemical and biological profile of water. WATER CYCLE A biogeochemical cycle that tracks the movement of water through earth systems. WATER EFFICIENCY Meeting human needs with the minimum amount of water necessary.