<P> A watermill or water mill is a mill that uses hydropower . It is a structure that uses a water wheel or water turbine to drive a mechanical process such as milling (grinding), rolling, or hammering . Such processes are needed in the production of many material goods, including flour, lumber, paper, textiles, and many metal products . These watermills may be comprise gristmills, sawmills, paper mills, textile mills, hammermills, trip hammering mills, rolling mills, wire drawing mills . </P> <P> One major way to classify watermills is by wheel orientation (vertical or horizontal), one powered by a vertical waterwheel through a gear mechanism, and the other equipped with a horizontal waterwheel without such a mechanism . The former type can be further divided, depending on where the water hits the wheel paddles, into undershot, overshot, breastshot and pitchback (backshot or reverse shot) waterwheel mills . Another way to classify water mills is by an essential trait about their location: tide mills use the movement of the tide; ship mills are water mills onboard (and constituting) a ship . </P>

What is the purpose of a water mill
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