A watermill is a mill driven by water. Moving water — a river or a stream — pushes a big wheel round, the wheel turns machinery inside the building, and the machinery does work. Most often the work was grinding grain into flour, but watermills also sawed wood, hammered iron and drove early factory machines. The important thing for a learner: 'mill' is doing two jobs at once in this word. A mill is the machine that grinds, and a mill is also the building it stands in. So a watermill can be the wheel-and-machinery, or the whole stone building by the river. Usually people mean the building. The word points backwards in time. Watermills powered Europe and China for well over a thousand years, and then steam and electricity replaced them. Today most watermills are old buildings kept for visitors, or turned into houses and restaurants. So when you meet the word, expect history, the countryside and something picturesque. It is not a modern industry word — for making electricity from water today, people say 'hydroelectric power' or 'a hydroelectric dam', not watermill. Compare it with its sister word 'windmill', which does the same job with wind instead of water. The pattern is clear once you see the pair.

水車磨坊、水力磨坊（用水流推動水輪來磨麥子的建築）。注意台灣說的「水車」有時指灌溉用的取水輪，那個英文是 waterwheel，不是 watermill。