The Comprehensive Assessment of Water Management in Agriculture drew on the work of 700 scientists:
The causes of water scarcity are essentially identical to those of the food crisis. There are serious and extremely worrying factors that indicate water supplies are steadily being used up.
Essentially every calorie of food requires a liter of water to produce it. Thus those of us on western diets, use about 2500-3000 liters per day. [up to 800 gallons each]
A further 2.5 billion people by 2030 will mean that we have to find over 2000 more cubic kilometers of fresh water to feed them. [finding nearly 500 cubic miles of new water supplies!]
This is not any easy task given that current water usage for food production is 7500 cubic kilometers and supplies are scarce. [story]