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Huge freshwater reservoir under the ocean off Hawaii

By Krista Charles

Lava rock and coast near Pueo Bay, Hawaii

Design Pics Inc / Alamy

A huge reservoir of fresh water under the ocean floor off the west coast of Hawaii’s Big Island could increase the risk of drought for the people living there.

Eric Attias of the University of Hawaii and his colleagues discovered the reservoir, which is contained in porous rock and lies at least 500 meters below the sea floor, using an imaging technique similar to an MRI scan.

They used a boat that dragged a 40-meter antenna behind it to create an electromagnetic field that sent electrical current through the ocean and under the ocean floor. Since seawater is a better conductor than freshwater, the team was able to distinguish between the two. They found that the reservoir extends at least 4 kilometers from the coast and contains 3.5 cubic kilometers of fresh water.


Most of Hawaii’s freshwater comes from onshore aquifers, which are subterranean rock and soil layers that collect water after rainfall. The team believes that water from these aquifers will replenish this newly discovered reservoir.

Climate change has led to increasing periods of drought in many places, which could leave some areas without water. In Hawaii, lower rainfall and destruction of forests could cause aquifers to dry up on land.

Not only would the offshore reservoir help alleviate the drought, it could also be easier to pump than the onshore aquifers because the water is under high pressure. Access to it would also have minimal impact on the surrounding ecosystems, says Attias.

Similar water caches could be located in front of other volcanic islands, the team says, which could bring relief to other places threatened by water scarcity due to climate change.

New sources of fresh water are usually discovered by drilling to take samples, but the new imaging technique from Attias and his colleagues could make that process easier and cheaper, says Kerry Key of Columbia University in New York.

Journal reference: Science Advances, DOI: 10.1126 / sciadv.abd4866

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