MIT's Technology Review has an article on San Diego's current state of the art desalination plant.
Desalination out of Desperation
Severe droughts are forcing researchers to rethink how technology can increase the supply of fresh water.
By David Talbot on December 16, 2014
One of the graphics shown is the amount of power used to produce a cubic meter (264 gals) of water.
What the article doesn't mention is the amount of water consumed to generate power in San Diego. The DOE has a paper you can check out on water use in thermoelectric power generation. 67% of SD power comes for natural gas plants. 24% renewable
“Each kWh of thermoelectric generation requires approximately 25 gallons of waterd, primarily used for cooling purposes – a 500 MW power plant would use approximately 300 million gallons of water per day. However, power plants also use water for operation of pollution control devices such as flue gas desulfurization (FGD) technology as well as for ash handling, wastewater treatment, and wash water. When discussing water and thermoelectric generation, it is important to distinguish between water use and water consumption. Water use represents the total water withdrawal from a source and water consumption represents the amount of that withdrawal that is not returned to the source.”
Here is a graphic to show the areas of water use in thermoelectric power plant.
For an example of thinking about water use in the data center check out this Google video on the use of gray water.