Why don't we get all our electric power from water?

   While the water is free, the dams to trap it and the machinery to exploit it are not. In fact, they are very costly. As an example, Fort Peck Dam in Montana has nearly 40 times as much solid mate­rial, by volume, as the Great Pyramid of the ancient Egyptian king Khufu. The number of good hydroelectric sites is limited, and many of them are a long way from the places where power is wanted. Even with modern methods of transmitting electric power, the cost rises with distance.