Watermill

A watermill is an engine that uses a water wheel or turbine to drive a mechanical process such as flour or lumber production, or metal shaping (rolling, grinding or wire drawing). A watermill that only generates electricity is more usually called a hydroelectric plant.
History
China
In 31 AD, a Chinese engineer named Du Shi (Wade-Giles: Tu Shih) "invented the first water-powered bellows. This was a complicated machine with gears, axles, and levers that was powered by a waterwheel,". This invention aided the forging of cast iron smelted from the blast furnace. More extensive descriptions appear in literature of the 5th century.
Greece and Rome
The ancient Greeks and Romans used the technology. In the 1st century BC, the Greek epigrammatist Antipater of Thessalonica was the first to make a reference to the waterwheel. He praised it for its use in grinding grain and the reduction of human labor.
The Romans used both fixed and floating water wheels and introduced water power to other countries of the Roman Empire. So-called 'Greek Mills' used water wheels with a vertically mounted shaft. A "Roman Mill" features a horizontally-mounted shaft. Greek style mills are the older and simpler of the two designs, but only operate well with high water velocities and with small diameter millstones. Roman style mills are more complicated as they require gears transmit the power from a shaft with a horizontal axis to one with a vertical axis. An example of a Roman era watermill would be the early 4th century site at Barbegal in southern France, where 16 overshot waterwheels were used to power an enormous flour mill.
The Cistercian Order built huge mill complexes all over Western Europe during the medieval period.
Medieval Europe
In a 2005 survey the scholar Adam Lucas identified the following first appearances of various industrial mill types in Western Europe. Noticeable is the preeminent role of France in the introduction of new innovative uses of waterpower.
Operation of a watermill
Typically, water is diverted from a river or impoundment or mill pond to a turbine or water wheel, along a channel or pipe (variously known as a flume, head race, mill race, leat, leet, lade (Scots) or penstock). The force of the water's movement drives the blades of a wheel or turbine, which in turn rotates an axle that drives the mill's other machinery. Water leaving the wheel or turbine is drained through a tail race, but this channel may also be the head race of yet another wheel, turbine or mill. The passage of water is controlled by sluice gates that allow maintenance and some measure of flood control; large mill complexes may have dozens of sluices controlling complicated interconnected races that feed multiple buildings and industrial processes.
Watermills can be divided into two kinds, one with a horizontal waterwheel on a vertical axle, and the other with a vertical wheel on a horizontal axle. The oldest of these were horizontal mills in which the force of the water, striking a simple paddle wheel set horizontally in line with the flow turned a runner stone balanced on the rynd which is atop a shaft leading directly up from the wheel. The bedstone does not turn. The problem with this type of mill arose from the lack of gearing; the speed of the water directly set the maximum speed of the runner stone which, in turn, set the rate of milling.
Types of watermills
Gristmills grind grains into flour. These were undoubtedly the most common kind of mill.
Fulling mills or Walkmills were used for a finishing process on cloth (see also fulling).
Blade mills were used for sharpening newly made blades.
Sawmills cut timber into lumber
Barking mills stripped bark from trees for use in tanneries
Spoke mills turned lumber into spokes for carriage wheels.
At the beginning of the industrial revolution, cotton mills were usually powered by a water wheel.
Carpet mills for making rugs were sometimes water-powered.
Textile mills for weaving cloth were sometimes water-powered.
Powder mills for making black powder or smokeless powder were sometimes water-powered.
Blast Furnaces, finery forges, slitting mills, and tinplate works were until the introduction of the steam engine invariably water powered and were sometimes called iron mills.
Prior to the introduction of the cupola (a reverberatory furnace), lead was usually smelted in smelt mills.
Paper mills used water not only for motive power but also in large quantities in the manufacturing process.