water mill

Machine that harnesses the energy in flowing water to produce mechanical power, typically for milling (grinding) grain. Water from a stream is directed against the paddles of a water wheel to make it turn. Simple gearing transfers this motion to the millstones. The modern equivalent of the water wheel is the water turbine, used in hydroelectric power plants.

Although early step wheels were used in ancient China and Egypt, and parts of the Middle East, the familiar vertical water wheel came into widespread use in Roman times. There were two types: undershot, in which the wheel simply dipped into the stream, and the more powerful overshot, in which the water was directed at the top of the wheel. The Domesday Book records over 7,000 water mills in Britain. Water wheels remained a prime source of mechanical power until the development of a reliable steam engine in the 1700s. Water power was used not only for milling but also for metalworking, crushing and grinding operations, and driving machines in the early factories. Steam power and the water wheel were combined to form paddlewheel steamboats in the 18th century.