People are tapping the world's supply of fresh water faster than it is being replenished, and if the trend continues they will be consuming 70% of available water by 2025.
The authors of a new report in the journal Science, including Stanford biologist Paul Ehrlich, who wrote the best-selling book "Population Bomb," warn that scarce water is already accelerating the spread of food shortages, international tension, disease and severe environmental degradation.
Global consumption of fresh water has tripled since 1950 and people are using 54% of accessible runoff, says the report in the Feb. 9 edition of Science.
It will be difficult to increase supplies, the authors say, because "fresh water constitutes only 2.5% of the total volume of water on Earth, and two-thirds of this is locked up in glaciers and ice caps." According to the study, less than 1% of fresh water is in aquifers, lakes, rivers, plants, the atmosphere and other places from which humans can derive its benefits.
At the same time, inefficient irrigation practices, massive pollution and subsidies that price water well below its value promote worldwide waste. For example, an estimated 95% of the world's urban areas dump raw sewage into rivers and other bodies of water.
The report maintains that desalination and other techniques for distilling, treating and transporting fresh water long distances are too expensive to help all but the most arid, energy-rich countries in the foreseeable future.
The study bolsters recent arguments by the World Bank and other experts that water shortages loom as one of the most critical problems facing the world in the next century. A World Bank report released in August said the wars of the next century will be over water.
"We would generally fall in line with the view that scarcity is going to be a big deal," said Kate Fish, director of public policy at Monsanto Co., the chemical giant that is researching ways to develop crops that are less water-dependent.
"We certainly don't have the strategies or technologies in place now to balance off the current rate of consumption."
But others disagree with key conclusions of the just-released study in Science.
"The idea that we are reaching carrying capacity in terms of fresh water is completely off base," said Terry Anderson, an economist who has written extensively about water.
"They [the authors of the study] ignore the important role water marketing can play in encouraging conservation and increased supply," said Anderson, who is executive director of the Montana-based Political Economy Research Center, a conservative think tank.
In California, water marketing allows farmers to make a greater profit by selling water to urban areas than they would by using the water to grow certain crops.
But Anderson agreed with other aspects of the study. "They are essentially correct in what they are saying about rates of human consumption."
Besides Ehrlich, the authors of the study are Sandra L. Postel, an environmental scientist and director of the Global Water Policy Project in Cambridge, Mass., and Stanford biologist Gretchen C. Daily.
In their study, the three researchers divided fresh water into two categories, with runoff providing the most accessible supply. The study found that only 30% of all runoff is available for irrigated agriculture, industry, domestic use, and for replenishing streams and wetlands to sustain fish and wildlife.
Most runoff is flood water that isn't captured by dams or else is too remote from human activities to be useful.
Use of runoff for agricultural or urban purposes tripled between 1950 and 1990. Now, people use about 54% of the available supply; that is expected to increase to 70% by 2025.
That could threaten food security, Postel said, because irrigated lands, which produce about 35% of the world's food, are no longer increasing as fast as the population and are not likely to catch up.
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Worldwide Water Crisis
Almost 80 countries, with 40% of the world's population, are experiencing water shortages that threaten their agriculture, industry and health, says the World Bank, the largest international funder of water projects. Today, 1 billion people lack access to clean drinking water in the developing world and 1.7 billion do not have adequate sanitation facilities. The United Nations estimates say that dirty water causes 80% of the disease in developing countries and kills 10 million people annually. Here is a look at world water resources.
The world's population is growing rapidly, especially in urban areas, from 5.6 billion today to 8 billion in 2025.
The supply of good-quality water is being contaminated through pollution originating from domestic wastes, industry, agricultural chemicals and mismanaged land use-effectively decreasing the amount of water available.