Most people may drink only two litres of water a day, but they consume about 3,000 if the water that goes into their food is taken into account. The rich gulp down far more, since they tend to eat more meat, which takes far more water to produce than grains.
So as the world’s population grows and incomes rise, farms will (if they use today’s methods) need a great deal more water to keep everyone fed: 2,000 more cubic kilometres a year by 2030, or over a quarter more than they use today.
Yet in many farming regions, water is scarce and likely to get scarcer as global warming worsens. The world is facing not so much a food crisis as a water crisis.
The solution, is more efficient use of water (Pivot Irrigation Systems) or, "more crop per drop”. Some 1.2 billion people, about a fifth of the world’s population, live in places that are short of water. Farming accounts for roughly 70% of human water consumption.
So when water starts to run out, as is happening in northern China, southern Spain and the western United States, among other places, farming tends to offer the best potential for thrift. But governments, whether to win votes or to protect the poor, rarely charge farmers a market price for water. So they are usually more wasteful than other consumers—even though the value they create from the water is often less than households or industry would be willing to pay for it.