Water wheel

from wikipedia:

A water wheel is a means of extracting power from the flow (or fall) of water, that is hydropower. Water wheels were widely used in the Middle Ages to power industry in Europe. The alternatives were the windmill and human and animal power. 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.

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