I would just like to point that your view appears to be very US centric -- not that this is a problem -- but I had in mind other areas like Greenland and Siberia as well.
Aquifer depletion is a significant problem and that is why I put the 'IF' in my statement. I presumed (without knowing) that undepleted aquifers can be found in the North and therefore provide an additional 50 years of reliable water supply for irrigation. Orthodoxy is not a religion.
In general, underground water sources in the US have been discovered and are undergoing depletion. In specific - to my knowledge - there is only one major source that hasn't been developed west of the Mississippi in the US. That source is brackish thus requiring a good deal of energy to allow it to be used. Outside the US? Again, I don't really know but I suspect they have been found and are being depleted (thinking of the Aral Sea) as well wherever agriculture is currently, or has been, practiced.
you are the media you consume.
