Water woes

Essentially, civil engineers can employ this technology to decouple water supplies from sanitation systems, a move that could save significant amounts of freshwater if it were more widely employed. Moreover, recycled waste could cut the use of fertilizer derived from fossil fuels.

Beyond constraining demand for freshwater, the opposite approach, increasing its supply, will be a critical component of the solution to water shortages. Some 3 percent of all the water on the earth is fresh; all the rest is salty. But desalination tools are poised to exploit that huge source of salty water. A recent, substantial reduction in the costs for the most energy-efficient desalination technology—membrane reverse-osmosis systems—means that many coastal cities can now secure new sources of potable water.

During reverse osmosis, salty water flows into the first of two chambers that are separated by a semipermeable (water-passing) membrane. The second chamber contains freshwater. Then a substantial amount of pressure is applied to the chamber with the salt solution in it. Over time the pressure forces the water molecules through the membrane to the freshwater side.

Engineers have achieved cost savings by implementing a variety of upgrades, including better membranes that require less pressure, and therefore energy, to filter water and system modularization, which makes construction easier. Large-scale desalination plants using the new, more economical technology have been built in Singapore and Tampa Bay, Fla.

Scientists are now working on reverse-osmosis filters composed of carbon nanotubes that offer better separation efficiencies and the potential of lowering desalination costs by an additional 30 percent. This technology, which has been demonstrated in prototypes, is steadily approaching commercial use. Despite the improvements in energy efficiency, however, the applicability of reverse osmosis is to some degree limited by the fact that the technology is still energy-intensive, so the availability of affordable power is important to significantly expanding its application.

A Return on Investment
Not surprisingly, staving off future water shortages means spending money—a lot of it. Analysts at Booz Allen Hamilton have estimated that to provide water needed for all uses through 2030, the world will need to invest as much as $1 trillion a year on applying existing technologies for conserving water, maintaining and replacing infrastructure, and constructing sanitation systems. This is a daunting figure to be sure, but perhaps not so huge when put in perspective. The required sum turns out to be about 1.5 percent of today’s annual global gross domestic product, or about $120 per capita, a seemingly achievable expenditure.

Unfortunately, investment in water facilities as a percentage of gross domestic product has dropped by half in most countries since the late 1990s. If a crisis arises in the coming decades, it will not be for lack of know-how; it will come from a lack of foresight and from an unwillingness to spend the needed money.

There is, however, at least one cause for optimism: the most populous countries with the largest water infrastructure needs—India and China—are precisely those that are experiencing rapid economic growth. The part of the globe that is most likely to continue suffering from inadequate water access—Africa and its one billion inhabitants—spends the least on water infrastructure and cannot afford to spend much; it is crucial, therefore, that wealthier nations provide more funds to assist the effort.

The international community can reduce the chances of a global water crisis if it puts its collective mind to the challenge. We do not have to invent new technologies; we must simply accelerate the adoption of existing techniques to conserve and enhance the water supply. Solving the water problem will not be easy, but we can succeed if we start right away and stick to it. Otherwise, much of the world will go thirsty.