Hi Leadhead

These are the 2 options I thought about

1) Don't bother and have a separate connection for you water pump. Switch it on manually before starting the CNC/VFD. This is what I have done
2) Or operate it through the break-out board on your cnc controller using a relay. You would then issue some Gcode to start the pump before the spindle start Gcode

Hope this helps
Mike