Select your localized edition:

Close ×

More Ways to Connect

Discover one of our 28 local entrepreneurial communities »

Be the first to know as we launch in new countries and markets around the globe.

Interested in bringing MIT Technology Review to your local market?

MIT Technology ReviewMIT Technology Review - logo


Unsupported browser: Your browser does not meet modern web standards. See how it scores »

{ action.text }

Supply-Side Options

Preventing water scarcity from undermining food security, ecological life-support systems, and social stability will not be easy. In much of the world, expanding the water supply for one user now means taking it away from another. New groundwater wells may expand supplies in some regions, but groundwater use will need to be reduced to the level of recharge in others. New dams and river diversions will rarely offer sustainable solutions, because in most cases they entail drawing more water from freshwater systems that are already overtaxed. In fact, the construction of new dams has slowed markedly over the last couple of decades as the public, governments, and financial backers have begun to pay more attention to their high economic, social, and environmental costs. Whereas nearly 1,000 large dams began operation each year from the 1950s through the mid-1970s, the number dropped to about 260 annually during the early 1990s. Even if conditions become more favorable to dam construction, it seems unlikely that new reservoirs built over the next 30 years will increase accessible runoff by more than 10 percent while population is projected to expand by 45 percent during that period.

Another option, desalination, is often held up as the ultimate solution to the world’s water problems, since the oceans hold more than 97 percent of the earth’s water. As early as 1961, President John F. Kennedy noted that if humanity could find an inexpensive way to obtain freshwater from the seas, the achievement “would really dwarf any other scientific accomplishment.”

Some 35 years later, desalination is a proven technology experiencing solid growth. As of December 1995, a total of 11,066 desalting units had been installed or contracted for worldwide, with a collective capacity of 7.4 billion cubic meters per year.

Despite considerable growth, however, desalination still plays a minor part in the global supply picture, accounting for less than 0.2 percent of world water use. Removing salt from water either by heating it and condensing the steam (distillation) or by filtering it through a membrane (reverse osmosis) is highly energy intensive. And although costs have come down to $1.00-$1.60 per cubic meter, desalination remains one of the most expensive supply options. The wealthy countries of Saudi Arabia, United Arab Emirates, and Kuwait-which together encompass only 0.4 percent of world population-accounted for 46 percent of the world’s 1993 desalting capacity. These countries are essentially turning oil into water, and they are among the few that can afford to do so. For the foreseeable future, seawater desalination will likely continue to be a lifeline technology for water-scarce, energy-rich countries as well as island nations with no other options. But desalination capacity would have to expand 30-fold to supply even 5 percent of current world water use. As such, the option will likely remain a minor contributor to total water supplies worldwide.

Other options, such as towing icebergs, transporting water by tanker, or shipping it in large bags, may increase drinking water supplies in some specific water-scarce areas, but like desalination, are expensive and not likely to make much of a dent in the global supply picture over the next 30 years.

Cutting Demand

Measures to reduce demand for water through conservation, recycling, and higher efficiency are typically more economical than efforts to gain new supplies of freshwater. Costing between 5 and 50 per cubic meter of water, nearly the entire spectrum of conservation options-including leak repair, the adoption of more efficient technologies, and water recycling-cost less than the development of new water sources and much less than desalination.

Unfortunately, large subsidies to water users continue to discourage investments in efficiency and convey the false message that water is abundant and can be wasted-even as rivers are drying up and aquifers are being depleted. Farmers in water-short Tunisia pay 5 per cubic meter for irrigation water-one-seventh the cost of supplying it. Jordanian farmers pay less than 3 per cubic meter, a small fraction of the water’s full cost. And federal subsidies to irrigators in the western United States total at least $20 billion, representing 86 percent of total construction costs of installing the systems, according to Richard Wahl, formerly an economist at the U.S. Department of Interior. Although poverty alleviation and other social goals may justify some degree of irrigation subsidy, especially for poor farmers, the levels of subsidization that exists today is an invitation to waste water.

Experience in the Broadview water district in California, where farmers irrigate 4,000 hectares of melons, tomatoes, cotton, wheat, and alfalfa, reveals the gains an intermediate policy can yield. In the late 1980s, when the district was faced with the need to reduce polluting drainage to the San Joaquin River, it established a tiered water pricing structure. The district determined the average volume of water used over the 1986-88 period and applied a base rate of $16 per acre-foot (1.3 per cubic meter) to 90 percent of this amount. Any water used above that level was charged at a rate 2.5 times higher. In 1991, only 7 out of the 47 fields in the district used any water charged at the higher level: the higher price encouraged farmers to switch crops and irrigate more efficiently, thus cutting the average amount of water applied to the district’s farms by 19 percent.

Because agriculture accounts for two-thirds of water use worldwide, even small-percentage reductions can free up substantial quantities of water for cities, ecosystems, and additional food production. Farmers in northwest Texas, for example, who have had to cope with falling water tables from depletion of the Ogallala aquifer-an underground water reserve in the region that gets extremely limited recharge from rainfall-have reduced their water use by 20 to 25 percent by adopting more efficient sprinkler technologies, special valves to ensure even water distribution, and other water-saving practices.

Likewise, results from a variety of countries show that farmers who have switched from furrow (trench) systems or sprinkler irrigation to drip systems, which deliver water nearer to the roots of crops, have cut their water use by 30 to 60 percent. Crop yields often increase at the same time because plants are effectively “spoon-fed” the optimal amount of water (and often fertilizer) when they need it. Drip systems, which cost in the range of $1,200 to $2,500 per hectare, tend to be too expensive for most poor farmers and for use on low-value row crops, but research is under way to make them more affordable. Colorado-based International Development Enterprises has developed a drip system that costs just $50 per half acre ($123 per half hectare), 10 to 20 percent of the cost of traditional drip systems. The keys to keeping costs down are simple materials and portability: instead of each row of crops getting its own drip line, a single line is rotated by farmers among ten rows.

Along with encouraging irrigation efficiency improvements, more appropriate water pricing would also promote the treatment and reuse of urban wastewater for irrigation, which is typically more expensive than most conservation and efficiency measures but often less expensive than developing new water sources. Wastewater contains nitrogen and phosphorus, which can be pollutants when released to lakes and rivers but are nutrients when applied to farmland. Moreover, unlike many other water sources, treated wastewater will be both an expanding and fairly reliable supply, since urban water use will likely double by 2025. Many large cities located along coastlines dump their wastewater, treated or untreated, into the ocean, rendering it unavailable for any other purpose and harming coastal marine life. As long as the wastewater stream is free of heavy metals and harmful chemicals, and disease-causing microorganisms are controlled, it can become a vital new supply for irrigating crops.

0 comments about this story. Start the discussion »

Tagged: Computing

Reprints and Permissions | Send feedback to the editor

From the Archives


Introducing MIT Technology Review Insider.

Already a Magazine subscriber?

You're automatically an Insider. It's easy to activate or upgrade your account.

Activate Your Account

Become an Insider

It's the new way to subscribe. Get even more of the tech news, research, and discoveries you crave.

Sign Up

Learn More

Find out why MIT Technology Review Insider is for you and explore your options.

Show Me