An approach to water purification, called forward osmosis, can treat far dirtier water than reverse osmosis, often using significantly less energy. The technique now treats some of the most challenging industrial wastewaters, provides emergency hydration and could bring relief to some of the world’s most water scarce regions, reports the U.S. Public Broadcasting Service.

Reverse osmosis requires pressurization to coax freshwater through membranes, a process that requires a significant amount of energy. By contrast, forward osmosis saves energy by relying on the natural tendency of water to flow through a semi-permeable membrane from concentrated to less concentrated solutions, eventually equilibrating the two.

Some 21 billion gallons of fresh water—enough to meet the needs of 300 million people—is desalinated worldwide each day, reports say. Most of that water comes from reverse osmosis. However, to coax freshwater through membranes in reverse osmosis, the seawater has to be pressurized, a process that still requires a significant amount of energy.

This is where forward osmosis comes in. Instead of pressurizing water and pushing it through a membrane, forward osmosis relies on the natural tendency of water to flow through a semi-permeable membrane from concentrated to less concentrated solutions, eventually equilibrating the two. “Instead of using pressure, we are letting nature do its job,” says Jim Matheson, CEO of Oasys Water. “It’s the way your body uses osmosis to move water for cellular processes.”

To reduce energy requirements of forward osmosis, researchers are now pursuing a number of novel techniques, including nanoparticles that can be filtered out, metallic salts that can be drawn out with a magnetic field and oil based salts that can be skimmed off the top of the water column to remove salt from their draw solution.

A 2014 study by researchers at the Massachusetts Institute of Technology (MIT)concluded that the energy requirements of forward osmosis will always be greater than those of reverse osmosis for seawater desalination. “In forward osmosis you are moving water into something more concentrated,” says study co-author Ronan McGovern, a postdoc at MIT. “It will always require more energy than reverse osmosis.”

At the same time, the scale up of reverse osmosis desalination has made it a very inexpensive method of water purification. “You can get 1,000 liters of water for less than $1 using reverse osmosis,” says Menachem Elimelech, a professor of environmental engineering at Yale University and one of the researchers behind the initial development of Oasys Water’s technology. “It’s very difficult at this stage to beat that.”

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