Man-Made Water

Freshening up: Salt water begins desalination process in plant south of Tel Aviv, Israel. Jim Hollander /epa /Corbis

As population growth, food production, and the regional effects of climate change place greater stress on the Earth's natural water supply, "man-made" water—created by removing salt from seawater and brackish groundwater through reverse osmosis desalination—will become an increasingly important resource for millions of humans, especially those in arid regions such as the Middle East, the western U.S., northern Africa, and central Asia. But its use will bring changes to the environment.

"Water that's been desalted through reverse osmosis contains a unique composition, which will induce changes in the chemistry and ecology of aquifers and natural water systems it enters," says Avner Vengosh, associate professor of earth and ocean sciences at the Nicholas School of the Environment.

A new study by Vengosh and colleagues in France and Israel provides tools to identify and trace this man-made water as it mixes with natural water supplies and, over time, replaces natural waters in areas entirely dependent on desalination.

The study, published in the journal Environmental Science and Technology, details for the first time the isotope geochemistry—or chemical fingerprints—of the elements boron, lithium, strontium, oxygen, and hydrogen, which are found in seawater and brackish groundwater that have been desalinized through reverse osmosis.

Identifying these unique geochemical and isotopic fingerprints gives scientists and water-quality managers a new array of tools for tracing the presence and distribution of man-made fresh water in a region's soils, surface water, and groundwater, Vengosh says.

"As this water leaks into the environment through poor infrastructure or enters it directly through irrigation, it will be possible to use our new tracers to track the water back to its origin.

"It's sort of like a detective who collects fingerprints at the scene of the crime and matches them to the guilty suspect," he says.

Being able to trace water back to a desalinated source will allow local governments and water utilities to zero in on the problem of water loss and correct it more quickly and efficiently. Moreover, because desalted wastewater can be recycled through the environment and reused as a source of drinking water—a process already being used in southern California—the new tools would enable utilities and government agencies to trace the relative contribution of desalted water in their systems and to test the effectiveness of their water-treatment processes.