Following on from my request for information on de-ionised water, firstly let me thank all those who replied.
I'm delighted to say that the Fanuc Wire Eroder is now re-assembled and re-commissioned in my barn and is cutting a test pattern as I type this.
The ion exchange column within the machine was able to process the 200 litres of 'inital fill' water and is keeping the conductivity within limits - lucky bonus was a tub of anion mixed cation resin that I was unaware was part of the sale!
AWEM