'''Hydropower''' can be used to do [[electrical]] or [[mechanical]] work. It is made by taking water and using it to do useful work. Some of the work that it has been known to do is saw lumber, and grind grain. The water is usually transferred through a variety of ways; shafts, pulleys, wheels,cables and gears. The hydropower dates back to the Greeks who used vertical axis water wheels as early as 85 BC and horizontal axis wheels from 15 BC. The hydropower was the only source besides wind power to do useful work until the steam engine came along in the early 19th century.
A lot more can be found in the book on pages 409-415.