Watermill - How it Worked 

A watermill is a machine, that captures the power of water to turn a waterwheel that through shafts and gears turn the millstones and grind grain to flour.
A weir across the river, provides a supply of water to turn the waterwheel.
The water flows along a channel to the waterwheel. This channel is known as the head race.
The undershot waterwheel type is the most common. The flow of the water pushes the paddles located around the wheels rim, to rotate the waterwheel that through a horizontal shaft that passes through the mill wall, turns the pit wheel inside the mill.
Inside the mill on the ground floor, the pit wheel which has teeth on its rim turns the wallower gear wheel fixed to the main vertical shaft. Fixed to the main shaft is the larger gear wheel that drives the spindle which passes through the floor and turns the top millstone of a pair, the bottom stone is fixed.
Grain was delivered in bags, by horse and cart and lifted to the top floor.
Grain from the top floor falls down through a chute into the opening in the centre of the top millstone.
The mill stones are hidden inside a wooden case.
The grain is ground into flour between the stones, and goes down through a chute to the ground floor, where it is bagged. The bags of flour were used to feed livestock during the winter months.