The scarcity of renewable freshwater not only poses a long-term threat but has already begun taking a toll in many countries, especially where population has grown out of proportion to water resources. The United Nations Food and Agriculture Organization estimates that producing the food needed for a nutritious, low-meat diet requires about 1,600 cubic meters of water per person per year. In humid climates, virtually all of this could be provided directly to the soil by natural rainfall. But in drier regions and in those with distinct wet and dry seasons, a portion of the needed moisture would have to be supplied by irrigation water drawn from rivers, lakes, or aquifers. Estimating conservatively that a third of the 1,600 cubic meters per person would need to be supplied by irrigation, annual water demand for food-above and beyond what direct rainfall provides-would average about 530 cubic meters per person.Of course, countries have more than just food needs to meet. Estimates by Russian hydrologist Igor Shiklomanov suggest that worldwide household, municipal, and industrial water uses average about 240 cubic meters per capita per year. More widespread use of efficient technologies could reduce this level substantially, but the resulting savings would partially be offset by the more than 1 billion people now lacking minimum household water supplies and by rising affluence, which translates into higher water use. Assuming an average for household, municipal, and industrial uses of 200 cubic meters per capita per year, and adding this to the freshwater required for food production, yields a requirement of some 730 cubic meters per capita per year.
Unfortunately, in many, if not most, countries it is difficult to access and control more than 30 to 50 percent of runoff. Moreover, a portion of runoff must remain in rivers to dilute pollution and satisfy other “instream” needs. Thus the total amount of runoff must be 2 to 3 times higher than the amount required to meet irrigation, industrial, and household water demands, which works out to be approximately 1,700 cubic meters per person per year. Consequently, countries can be considered “water stressed” when the total annual runoff per capita drops below 1,700 cubic meters.
Some water analysts argue that this “water stress” indicator can be misleading. Hillel Shuval, professor of environmental science at Hebrew University, points out, for example, that Israel maintains a highly successful modern economy and high per-capita income even though its renewable water per person is less than a fifth of the water-stress level of 1,700 cubic meters per year. In part, Israel has succeeded so well with its limited supplies by importing much of its grain-which Shuval and others sometimes refer to as “virtual water.”
Indeed, with the production of each ton of grain requiring some 1,000 tons of water, importing grain becomes a key strategy for balancing water budgets. Such a strategy would seem to make economic and environmental sense for countries short of water, since they can get much higher value from their limited supplies by devoting them to commercial and industrial enterprises and using the resulting income to purchase food through international markets. The Middle East, for instance, which is the most concentrated region of water scarcity in the world, imports 30 percent of its grain. As long as surplus food is produced elsewhere, nations with surpluses are willing to trade, and the countries in need can afford to pay for the imports, it would seem that water-short countries can have food security without needing to be food self-sufficient.
This tidy logic is shaken, however, by the growing number of people living in countries where water availability is a constraint to food self-sufficiency, and by widespread signs of unsustainable water use in key food-producing regions. As of 1995, a total of 44 countries with a combined population of 733 million people had annual renewable water supplies per person below 1,700 cubic meters. Just over half of these people live in Africa or the Middle East, where the populations of many countries are projected to double within 30 years. Water-short Algeria, Egypt, Libya, Morocco, and Tunisia are each already importing more than a third of their grain. With their collective population projected to grow by 87 million people over the next 30 years, these countries’ dependence on grain imports is bound to increase. Indeed, this is a likely scenario for much of Africa: given current population projections, more than 1.1 billion Africans will be living in water-stressed countries by 2025-three-quarters of the continent’s projected population.
Portions of many large countries, including China, India, and the United States, would also qualify as water stressed if breakdowns of water supplies and population were available by region. Even using national statistics, China-with 7 percent of global runoff but 21 percent of world population-will narrowly miss the 1,700 cubic meter per capita mark in 2030; India, the world’s second most populous country, will join the list by then.