阅读理解。
The need to feed a growing population is putting much pressure on the world's supply of water. With 97%
of the world's water too salty to salty to be drunk or be drunk or used in agriculture, the worldwide supply of
water needs careful management, especially in agriculture. Although the idea of a water shortage (短缺) seems
strange to someone fortunate enough to live in a high rainfall country, many of the world's agricultural industries
experience constant water shortages.
Although dams can be built to store water for agricultural use in dry areas and dry seasons, the costs of
water redistribution (重新分配) are very high. Not only is there the cost of the engineering itself, but there is
also an environmental cost to be considered. Where valleys (山谷) are flooded to create dams, houses are lost
and wildlife homes destroyed. Besides, water may flow easily through pipes to fields, but it cannot be
transported from one side of the world to the other. Each country must therefore rely on the management of
its own water to supply its farming requirements.
This is particularly troubling for countries with agricultural industries in areas dependent on irrigation (灌溉).
In Texas, farmers' overuse of irrigation water has resulted in a 25% reduction of the water stores. In the
Central Valley area of southwestern USA, a huge water engineering project provided water for farming in dry
valleys, but much of the water use has been poorly managed.
Saudi Arabia's attempts to grow wheat in desert areas have seen the pumping of huge quantities of irrigation
(灌溉) water from underground reserves. Because there is no rainfall in these areas,such reserves can only
decrease, and it is believed that fifty years of pumping will see them run dry.