"There is no doubt that we need to rethink how we use water, especially with the human population growing rapidly, and global warming likely to produce unpredictable patterns of rainfall and drought. Nevertheless, my own research suggests that the situation may not be as dire as many are suggesting. Nations can thrive on surprisingly meagre quantities of fresh water - provided they adopt water-efficient technologies and encourage economic activity that doesn't guzzle water. I believe the looming water crisis is primarily a problem of distribution and management rather than supply. And we can solve it with existing technologies, increased investment and political will."
Certainly true: Agriculture consumes more than 80% of water resources in dry countries. The efficiency of irrigation averages at around 50%. Increasing the efficiency to 75% (very possible) will be akin to providing 50% more water.