For water wheels used to drive boats, see paddle wheel. For wheels used solely to lift water see noria. For factories or industries driven by water wheels see watermill.

An overshot water wheel standing 42 feet high powers the Old Mill at Berry College in Rome, Georgia

A water wheel is a hydropower system; a machine for extracting power from the flow of water. Water wheels and hydropower was widely used in the Middle Ages, powering most industry in Europe, along with the windmill. The most common use of the water wheel was to mill flour in gristmills, but other uses included foundry work and machining, and pounding linen for use in paper.