The first reference to water power in Ireland is attributed to King Cormac MacArt, in the third century the annals record that Cormac sent for a skilled man from ' Over the wide sea' to build him a mill. His purpose to save a favourite maid servant the drudgery of grinding at the quern. Cormac's mill was constructed on the stream of Nith, which flowed from the well of Neamhuach at Tara. This is generally accepted to be the first mill built in Ireland, it is thought the millwright was supplied by the king of Scotland.
Before the introduction of powered mills all the grain used was ground using the mortar and pestle principle, later a saddle quern was used this was a saddle shaped stone on which the grain was placed another stone was rolled and dragged across the grain crushing it.
The next development was the rotary quern, this was essentially two circular stones the bottom one had an trunion of sorts in the centre of it, the top had a hole larger than the trunion pin, the top stone was pushed too and fro by means of a handle set to the side, the grain was placed in the hole and emerged at the sides as flour.
This is exactly how powered mills operate except that the top mill stone rotates continuously.