CAMBRIDGE - Around the world, demand for fresh water doubles every 20 years, owing to increasing population and affluence. Yet pollution, climate change, and seawater intrusion are diminishing supplies of fresh water at similar rates. So, is a global fresh water crisis looming?
Fortunately, the situation appears to be less alarming. This is not to deny that the supply of fresh water is getting tight. Left unattended, major disruptions for human society could occur.
Many argue that water is different from resources such as oil, because there are often no substitutes for water in most uses (particularly growing food). Moreover, water is an essentially fixed resource, albeit one that renews itself every year.
There are prodigious quantities of water on the globe, but most of it is salty ocean water and brackish groundwater. There are huge resources of fresh water, but most is in ice sheets and glaciers, with only a small percentage readily available where and when we need it. The supply of water is also highly variable across regions and within countries, with floods and droughts occurring at irregular times.
One new factor influencing water supplies is rising global temperature. Although we are not certain about the exact effects, many scientists believe that total annual precipitation will increase, but that its seasonality and the frequency of extremes may also increase. This would make it difficult to use the existing supply infrastructure of dams, reservoirs, treatment systems, and pipelines without big modifications.
From the writings of the earliest modern commentators on the drivers of socio-economic growth and decline - Adam Smith, Edward Gibbon, Thomas Malthus, David Ricardo, and Karl Marx - we see that concern about exhausting resources is not new. Malthus and Ricardo were particularly prescient about the roles of population, food, and energy resources.
Malthus postulated a geometric rate of population growth (like compound interest on a bank deposit) and an arithmetic rate of growth (simple interest on a bank account) of food production. These curves always intersect after a couple of decades, and Malthus predicted widespread famine or violent conflicts: food and population would be aligned with each other by "misery, war, pestilence, and vice."
Ricardo projected "declining returns" on investments in resources, whereby the best (least-cost) resources are used first, followed by the next best, and so on. Increasing demand for resources leads to price increases that will continue until the resource becomes too expensive to use.
Of course, these constraints were at work over previous centuries, before Malthus and Ricardo articulated them, but homo sapiens was able to "cheat" by expanding our resource base (colonialism) to bring in cheaper resources and food; by finding substitutes for scarce resources; and by improving our technology so that the same amounts of land and resources could be used more efficiently.
Because the world is now pretty much filled up, there are few opportunities to expand the physical supply of resources. The real question now facing the planet is whether we can continue improving our technologies or finding cheaper substitutes. Just because something worked over the past 200 years does not mean that it will necessarily continue to work. This is the crux of the problem facing global water resources.
But we can avoid a crisis by embracing the following technical and managerial adaptations:
- Trade virtual water - the amount of water that is embodied in producing a product (usually food) and shipping it somewhere else to be used. This saves the recipient from using his own water, which can be saved for higher-value activities;
- Conserve irrigation water. Because agriculture routinely accounts for 75-90% of all water consumed in a country, a 10% efficiency gain would save as much water as all the water used by the country's municipalities and industry. Another way of improving irrigation efficiency is by developing crops that produce more food with the same, or less, water. Research on such genetically modified (GM) foods is well advanced in several of the largest water-scarce countries, such as China and India*;
- Exploit advanced desalination. Modern developments in desalination have brought the cost per unit of desalinated seawater to levels comparable to obtaining fresh water from natural sources (approximately US$0.05 per cubic meter).
- Expand wastewater recycling. Urban areas typically dispose of about 85% of their fresh-water intake as wastewater, often in neighboring water bodies. The wastes could be treated and used to replenish groundwater. Emerging low-water-using sanitation technologies such as urine-separating dry-composting toilets could also significantly reduce urban water demands if properly developed;
- Develop creative pricing policies for urban water and wastewater. Protecting human and ecosystem health are difficult to price, because they form part of the pervasive externalities associated with water use. Nevertheless, many water uses would respond well to more efficient prices.
Although avoiding a global water crisis will not be easy, we have at hand policies and technologies that, if properly applied, could see us safely through the next several decades, even in the face of increasing - and increasingly wealthy - populations.
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