1791

Desalination

Thomas Jefferson (1743–1826)

Fresh (non-salty) water represents less than 3 percent of the world’s water supply, and more than two thirds of that is locked up in glaciers, polar caps, and deep crustal groundwater. This leaves only a very tiny fraction of Earth’s water (mostly in lakes, rivers, and shallow underground aquifers) potentially available for plants, animals, and human consumption and farming. With a growing global population and an increasing fraction of that small supply suffering from pollution and/or dwindling from overuse, the world is currently in a freshwater crisis. The United Nations estimates, for example, that 14 percent of the world’s population—more than a billion people—will encounter water scarcity by 2025.

Beyond recycling and conservation, another part of the solution to the world’s freshwater problems could be the removal of salt—desalination—from seawater, which is abundant on our planet. Desalination is an ancient concept and practice. The ancient Greeks, for example, knew that boiled seawater would condense as freshwater. Sailors in the Roman Empire would boil seawater onboard and capture and drink the condensed steam using sponges. Thomas Jefferson, George Washington’s secretary of state in 1791, researched and experimented on a variety of ways for sailors and other “sea-faring citizens” to desalinate seawater for drinking, and arranged for descriptions of the then-known desalination methods to be printed on the backs of all permits issued to ships departing from US ports.

Historical methods of desalination work reasonably well for small groups of people with modest freshwater needs, like sailors on a ship. They become problematic in terms of energy consumption and infrastructure, however, when the demand for freshwater becomes large, like that needed to sustain a farm or a city. Nonetheless, significant advances in desalination technology and efficiency have been made, especially in the last few decades, and especially in countries in arid regions such as the Middle East and Australia. These include methods such as reverse osmosis filtration, which uses electrically charged membranes without needing to heat/boil seawater—now the most commonly used and economical desalination method. Use of solar, wind, and even wave energy for electricity generation in those kinds of facilities is helping to make them less polluting and even more sustainable and economical.

1964 photo of the view of the Zarchin desalination plant on the Red Sea in Eilat, Israel.