> The pump is commonly powered by a windmill

Pretty much every farm in America before WWII, and many during the Fifties in seriously rural areas. I lived on a farm with a windmill that pumped water up to a big tank on stilts, and that was our household water. We didn't use it to generate electricity, though - just drinking and washing.

Windmills and water pumps to holding tanks are a centuries old, known technology. I'd be interested in how efficient generating electricity from the flow of the water is.