About 20 to 30 miles off the coast of Massachusetts, beneath the salty Atlantic Ocean, a team of scientists spent the summer of 2025 drilling into the seafloor. They were looking for something unusual: fresh drinking water.
By the time they finished, they had pulled up thousands of liters of water with salinity as low as 1 part per thousand. That puts it in the same range as many aquifers on land.
The discovery confirms a massive, hidden undersea aquifer stretching from New Jersey to Maine, according to Expedition 501, a $25 million international research collaboration. Early estimates suggest the reservoir could hold enough water to supply New York City for hundreds of years.
A 1976 Clue Led to a Systematic Search
The trail to this hidden water began nearly 50 years ago. In 1976, a U.S. government ship searching for oil and gas off the East Coast drilled into the seafloor. The crew found something strange: fresh water trickling out of the cores.
At the time, no one knew what to make of it.
Then, in 2015, researchers from the Woods Hole Oceanographic Institution and Columbia University used electromagnetic technology to map the area. They found evidence of a “massive offshore aquifer system” that might rival the Ogallala aquifer, the vast freshwater reserve that supplies parts of eight Great Plains states.
Expedition 501 became the first systematic drilling campaign designed to confirm that water and bring samples back.
What the Expedition Found
From May to July 2025, researchers aboard the Liftboat Robert a platform that normally services oil rigs and wind farms drilled at three sites in water depths of about 40 to 50 meters. They bored as deep as 550 meters below the seafloor.
The team found fresh or nearly fresh water at both shallower and deeper depths than expected. That suggests the supply may be even larger than earlier estimates.
“Four parts per thousand was a eureka moment,” Brandon Dugan, a geophysicist and hydrologist at the Colorado School of Mines and the expedition’s co-chief scientist, told the Associated Press. That salinity level, measured early in the drilling, hinted that the water was connected to a land-based system in the past. Possibly it still is.
At some sites, salinity dropped to 1 part per thousand. For comparison, the average salt content of ocean water is about 35 parts per thousand.
The expedition collected nearly 50,000 liters (about 13,200 gallons) of water. Dozens of labs around the world are now analyzing it.
Three Theories for How the Water Got There
No one knows for sure where this water came from. The scientific prospectus for the expedition, published in November 2025, lays out three main ideas.
First, the water may be ancient rainwater that seeped into the ground during the Pleistocene epoch, when sea levels were much lower and the continental shelf was dry land. Second, it could be meltwater that ran under ice sheets during the Last Glacial Maximum, when the Laurentide ice sheet covered much of North America. Third, it might have come from pro-glacial lakes that formed at the edges of retreating ice.
The water’s age will tell researchers whether it is a renewable resource. Young water would mean the aquifer is still recharging from land. Ancient, trapped water would mean the supply is finite.
“Younger means it was a raindrop 100 years ago, 200 years ago,” Dugan told the AP. “If young, it’s recharging.”
The Water Is Not Ready to Drink Yet
Before anyone can use this water, researchers have to answer some basic questions.
The water may contain minerals or microbes that could make people sick, according to Jocelyne DiRuggiero, a Johns Hopkins University biologist who studies microbial life in extreme environments. DiRuggiero, who was not part of the expedition, told the AP that the same processes that give us clean water in land aquifers are at work here. But no one has ever studied this undersea environment before.
Researchers are now sequencing DNA from their samples to figure out which microorganisms live there and how they survive.
Even if the water turns out to be safe and renewable, pulling it out of the ground on a large scale would be hard. Offshore drilling costs a lot of money. No one has clear rules about who owns undersea freshwater. And pumping could damage things in ways people do not expect.
“If we were to go out and start pumping these waters, there would almost certainly be unforeseen consequences,” Rob Evans, a Woods Hole geophysicist whose 2015 expedition helped map the aquifer, told the AP. Evans said pumping could disrupt nutrients that seep from the seafloor and feed local ecosystems. It could also pull water away from reserves on land.
