Hydrologist Malin Falkenmark and colleagues have calculated that, once a country's available water resources drop below 1,700 cubic meters per person per year, the country can be expected to experience regular water stress. Water stress means that for at least part of the year all water needs cannot be met without drawing down groundwater supplies or using surface waters faster than these resources are replenished (28). If the amount of water available per capita drops below 500 cubic meters per person per year, countries face conditions of absolute water scarcity (26, 28, 119).

Water scarcity or chronic stress make it difficult to expand agricultural production to keep pace with population growth. The amount of irrigated land available per capita and grain production per capita generally rise or fall together. From 1950 to 1980, for example, the amount of irrigated land per capita expanded, and grain production per capita increased. During the 1980s and 1990s, however, irrigated land per capita and grain production both have declined (9).

In 1990, 28 countries with a combined population of 335 million faced chronic water stress or outright scarcity. By 2025, 52 countries may face water shortages, affecting over 3 billion people—about 40% of the world's projected population (26, 119). The 20 countries of the Near East and North Africa face the worst prospects: annual per capita water availability already has fallen to only 1,250 cubic meters, 60% less than in 1960. By 2025 per capita supplies are projected to fall another 50%, to 650 cubic meters. Currently, Jordan and Yemen withdraw 30% more water from groundwater aquifers every year than is replenished (26, 73, 129).

Pollution. In many countries water pollution has contributed to water shortages and thus constrained food production, as well as caused health problems (133). For example, of 78 major rivers in China, 54 are seriously polluted. More than 40 of Malaysia's rivers are so fouled with municipal, industrial, and agricultural wastes that they are biologically dead (41). The nearly 450 cubic kilometers of wastewater that are discharged into surface waters every year require an additional 6,000 cubic kilometers of freshwater—two-thirds of the world's total stable water runoff—to dilute the waste-water and carry it to the oceans (133).

Some countries, such as Burkina Faso, where these women are carrying water drawn from a community well, face serious shortages of water. Water scarcity makes it more difficult to expand agricultural production and to keep pace with population growth.