The history of human civilization is entwined (交织) with the history of the ways we have learned to manipulate water resources. As towns gradually (67) , water was brought from increasingly sources, leading to (68) engineering efforts such as dams.
During the industrial revolution and population (69) of the 19th and 20th centuries, the demand for water rose (70) . Unprecedented construction of tens of thousands of engineering projects brought great (71) to hundreds of millions of people. Food production has kept (72) with soaring populations mainly because of the expansion of artificial irrigation systems that make possible the growth of 40% of the world’s food. Nearly one fifth of all the electricity worldwide is (73) by turbines (涡轮) spun by the power of falling water. Yet there is a dark side to this picture: (74) our progress, half of the world’s population still (75) , with water services access to those (76) to the ancient Greeks and Romans. As the United Nations report on access to water restated in November 2001, clean drinking water is (77) for more than one billion people; some two and a half billion do not have (78) sanitation (卫生) services. Prable water-related diseases kill a (an) (79) 10, 000 to 20, 000 children (80) , and the latest evidence suggests that we are (81) behind in efforts to solve these problems.
The (82) of our water policies extend beyond enering human health. Tens of millions of people have been (83) to move from their homes—often with little warning or (84) —to make way for the reservoirs behind dams. More than 20% of all freshwater fish (85) are now threatened or enered because dams and water withdrawals have destroyed the free-flowing river ecosystems where they (86) .