During the industrial revolution and population explosion of the 19th and 20th centuries, the demand for water rose dramatically. Unprecedented construction of tens of thousands of monumental engineering projects designed to control floods, protect clean water supplies, and provide water for irrigation and hydropower brought great benefits to hundred of millions of people. Food production has kept pace with soaring populations mainly because of the expansion of artificial irrigation system that make possible the growth of 40% of the world's food. Nearly one fifth of all the electricity generated worldwide is produced by turbines spun by the power of falling water.