But it's not only about the additional mouths to feed; it's also the growth of new appetites. Much of the growth in demand will emerge from the swelling sprawl of bustling, slum-pocked metropolises across the developing world. For the first time in history, the share of the global population living in cities recently surpassed 50 percent – on its way to 75 percent expected by 2050.
With each step up the economic ladder, people demand more water for sanitation, industry, hydroelectric power, and water-intensive diets – such as preferring beef to wheat, a shift that requires 10 times as much water per kilogram to produce. Urban-rural competition for water has already pushed countries to import grains – "virtual water" – or, in the case of wealthier countries like China, South Korea, and Saudi Arabia, to lease land in developing countries.
By 2030, the Water Resources Group forecasts, global water requirements may outstrip sustainable use by 40 percent. And almost half the world's people will be living under severe water stress, predicts the Organization for Economic Cooperation and Development (OECD).
Already, water stress – where the reliable water supply is being used up more quickly than it can be replenished – is widespread and is expected to increase significantly in the years ahead, particularly in North Africa, the Middle East, and Asia. By 2050, according to the UN's Food and Agriculture Organization, 1 in 5 developing countries will face water shortages.