Water travelled along a series of canals, througout Mylopotamos - ll interlinked. Water would fall from a height into a designated water mill wheel, turning the wheel, and then the stone, and hence crushing the wheat.
Mills were owned by individual families.
Those who grew wheat, but had no mills, would bring their wheat - often with great difficulty - to the mill on a designated day.
A week later - the miller would have the flour ready for "pick up".
Once the water had passed through a mill - it would move on - further down the canals, to "turn another mill".
The engineering principles involved were quite ingenious.