Watermills have been in existence since antiquity. Evidence exists for their use, by both the Romans and the Greeks, and from them the technology was spread throughout Europe. Vitruvius, the classical architect who would so greatly influence Leonardo da Vinci, created the first known diagram of a Watermill. By the middle ages, this technology was ubiquitous. The date of this event refers to the year of the Domesday book, a proto-census of England. The book showed, among other things, that in England alone there were 5,624 watermills, a number that would increase in the coming centuries. Thus when Leonardo experimented with watermills, it was an immensely practical study, one that could impact the lives of people across the continent. Overwhelmingly, these mills were used to grind grain, a staple of the European diet. However, in some cases there is evidence that the mills were used to power other industries, and this seemed to be increasingly the case as time went on. Leonardo’s own work would focus on expanding possible uses for the mill. The water mill, was one of the most important pieces of medieval machinery.

Thorkild Schhøler (1989) The Watermills at the Crocodile River: A Turbine Mill Dated to 345–380 a.d., Palestine Exploration Quarterly, 121:2, 133-143

https://en.wikipedia.org/wiki/Watermill#CITEREFGimpel1977

Picture by Pierre 79, retreived from Wikimedia Commons, fair use