In an interview released on March 26th, 2011, Lester Brown said says lots of interesting things, but the most urgent one is the current status of water supplies worldwide (emphasis mine):

Lester Brown: in looking at the global picture, it is water that is emerging as the principal constraint on efforts to expand food production. There’s a lot of land in the world that could provide us food, if there was water to go with it. And what we have seen is that there are countries whose rising demand for food have led them to over-pump aquifers and underground water resources. Now, you can over-pump in the short run. But once you’ve depleted the aquifer, then the rate of pumping is necessarily reduced to the rate of aquifer recharge from precipitation. So we’re looking at a situation where a number of countries have artificially inflated their grain production by over-pumping.

Scott Thill: And their bubbles are bursting.

Lester Brown: These bubbles are in countries that contain over half of the world’s people, and they’re starting to burst. The first is occurring in Saudi Arabia, which was self-sufficient in wheat production for twenty years but whose production has fallen by two-thirds in three years. They’re going to have to phase it out entirely in another year or two, because they were pumping a fossil aquifer, which is like an oil field. Once you pump it out, it’s gone. You’re going to see more of those.

Please do read the rest of the interview. For the record, this is why I say that one of the most important things about water is not if its managed as a public good, or as private/commercial product but if the data about water management are completely public.