"A coal fired plant uses 110 to 300 gallons per megawatt hour; a nuclear plant uses between 500 and 1100 gallons/MWh; and a solar parabolic trough plant uses 760 -920 gallons/MWh."

When Arizona exports electricity to California, it is essentially exporting a considerable amount of water--water allocated to Arizona under the Colorado River agreement but "wasted" in the cooling systems of the coal, nuke, and concentrated solar generating systems.
http://apps1.eere.energy.gov/states/energy_summary.cfm/state=AZ