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 center 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.
