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Watering the World

Seawater purification is one promising avenue

Some 300 million people around the world have to worry daily about such questions as, "Where will my next drink of water come from?" or "Where will I get water to grow my crops?" By a quarter of the way into the next century, that number is expected to grow to 3 billion water-hungry people.

How will the world meet its looming water crisis?

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Some solutions are obvious: Conserving the water we already use or recycling it cleanly. Or dig more wells, taking care not to deplete aquifers.

But one solution is making surprising progress, partly because many of the world's trouble spots include water shortage as a point of conflict. It's desalination, the cleaning of either seawater or brackish water through a variety of different technologies.

Desalination may offer some hope of resolving water disputes between Israel and the Palestinians. Already in the Persian Gulf, Saudi Arabia runs the world's largest plant for desalting seawater. The other Gulf states are equally committed to the technology. They have little choice, and they have plenty of one key resource: energy, in the form of oil. The Saudis and others can essentially turn oil into water, using their abundant energy source to power evaporation plants that produce potable water.

The lack of abundant energy is what limits the use of desalination in much of the rest of the world. Energy costs are often prohibitive. But the technology is improving. The most efficient method of desalination available today is called reverse osmosis. Water is forced, under pressure, through membranes that trap the salts and other impurities. These plants require significant amounts of energy too, but not as much as the evaporation technique, which typically operates in tandem with electricity production. Energy requirements for seawater reverse osmosis have dropped by half in a decade.

Step forward in the US

A big step in the increased use of reverse osmosis is being taken in the United States. Tampa Bay, Fla., is building a large plant that is expected to produce fresh water at a cost to consumers of about $2 per 1,000 gallons. That's roughly equivalent to the cost of water from traditional sources.

Experts are quick to say, however, that the cost-effectiveness of desalination depends on local conditions - for example, the ample supply of energy in Florida, the relatively low salt content of Tampa Bay waters, and the dwindling supplies of fresh water in the state's aquifers.

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Island countries are classic locales where desalination pays. Curacao, in the Netherlands West Indies, has relied on desalination for 70 years. Spain has invested in a number of large desalination plants along its coast, to help supply the tourist boom there. Israel is moving toward a similar investment, including, sensibly, a joint desalination venture with the Palestinians in Gaza. In the US, California, with its burgeoning coastal cities, will have to stop talking about desalination and actually do it.

But drawing on the endless oceans for drinkable water is no cure-all. At present, even with thousands of desalination plants worldwide and a $2 billion a year industry building and operating them, this method supplies less than 0.2 percent of the water used worldwide.

Needed: a multifaceted approach

The crises posed by expanding populations in sub-Saharan Africa and South Asia, by disputed surface supplies like the Jordan, the Tigris-Euphrates system, the Nile, and the Ganges, and by the extreme water-shortage problems facing northern China demand a multifaceted approach. More efficient agriculture, with much less reliance on field-flooding methods of irrigation, will be crucial. More and more waste water will have to be recaptured and cleaned up for reuse.

Not least, political leaders will have to learn how to negotiate water-sharing treaties that defuse water as a cause of war. The agreement between India and Bangladesh on dry-season flow in the Ganges is one hopeful example.

Desalination, like solar energy, is a technology that appeals to our idealism - exploiting a virtually inexhaustible resource to meet a basic human need. Some day it may provide a much greater portion of the world's water.

Meantime, there is no shortage of practical steps humanity can take to find the water it needs.

(c) Copyright 1999. The Christian Science Publishing Society

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