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A vast aquifer beneath the ocean floor could reshape how we think about water — on Nantucket and beyond.
In several spots roughly 20 to 40 miles south of Nantucket, beneath the same stretch of ocean now dotted with wind turbines, scientists drilled into the seafloor last summer in search of something unexpected: fresh groundwater.
Leading the expedition was Brandon Dugan, a geophysicist and hydrologist at the Colorado School of Mines and co-chief scientist of the International Ocean Drilling Programme. For about 74 days, he and his team worked aboard a massive offshore rig as part of a $25 million international collaboration involving 41 scientists from 16 countries and funded in part by the U.S. National Science Foundation, extracting sediment cores from deep beneath the ocean floor. They were testing a hypothesis: that vast reserves of freshwater are trapped in offshore sediments.
Dugan is not new to Nantucket; he previously worked with researchers at the U.S. Geological Survey and with the local water department to study the island’s groundwater system — research and models that helped inform questions about what might lie offshore.
What they found matched the team’s predictions: significant volumes of freshened groundwater are stored within sand and gravel beneath the seafloor some 20 to 40 miles off our shores. Scientists refer to this kind of water-bearing formation as an aquifer, essentially a layer of sediments that holds and transmits water. The team also confirmed the offshore aquifer stretches from New Jersey to Maine.
Dugan and his team also wanted to understand the sediments themselves: which layers would allow water to flow freely, which might trap it, and how the chemistry of the water in those sediments might vary. To do that, they collected nearly 50,000 liters of water for analysis.
“Think about going to the beach and digging a hole and it fills with water,” Dugan told me in an interview over Zoom earlier this year. “What does that water look like that was in those pores between those sediments?”
His team focused on two key measurements: how much salt the water contained, and how long it had been trapped in the sediments. This aquifer is one of many hidden pockets of “secret fresh water” beneath shallow oceans around the world, Dugan said — a resource that could one day help meet growing global water demand.
The choice to study this stretch of ocean didn’t come out of nowhere. Early drilling along the Atlantic margin in the 1960s and ‘70s had already documented freshwater offshore, but those studies were mostly descriptive, noting the water’s presence without quantifying it. Dugan and his team wanted a closer look: how much water was there, how old was it, how did it move, and could it be replenished over time?
“Most of us think of water as sort of an infinite resource,” Dugan said, “but in this case, likely because we’re surrounded and encapsulated by an ocean, it’s somewhat of a finite resource.” Understanding the origins and dynamics of this offshore aquifer will not only satisfy local curiosity and provide a potential future water source; it could also help scientists model similar systems elsewhere, from South Africa to New Zealand and Australia.
Dugan and his team drilled three sites, moving gradually farther from Nantucket’s coast to map the offshore aquifer. At the site closest to land, the water in the first sediments they reached looked much like the ocean above — salty, with about 32 practical salinity units (PSU), which is considered sea water salinity. But then they dug deeper, and some 80 meters (262 feet) below the seafloor, they hit a big “seal,” or low-permeability clay area, and the water flipped to just 1 PSU — fresh by drinking water standards. “It still needs to be treated for pathogens and things like that, but it meets general clean water standards, and we saw about 200 meters (656 feet) of that,” Dugan said. They observed freshened water in both clay seals and sandy aquifers. “So whatever put that water in there had enough energy to go through the easily flowing units, but also the units that it was hard to move water through, so [it] had to have a lot of energy.”
The pattern held farther offshore. At the second site, roughly 40 kilometers (24 miles) offshore, water in the sediments remained seawater for roughly 80 meters before dropping to about 4 PSU. “So a little saltier than the other water, but significantly less salty than seawater,” Dugan said. Again, the team saw roughly 200 meters of these lower-salinity layers.
At the farthest site, about 70 kilometers offshore, the trend repeated. The water was about half the salinity of seawater, much saltier than the freshened layers closer to shore, but still below normal ocean levels. “And that’s what we predicted from our original hypothesis. But now we have an idea of how quickly it goes from very fresh to mostly salty to all-the-way salty,” Dugan said.
Understanding this offshore aquifer isn’t just a matter of scientific curiosity; it has real implications for water management and climate resilience. Preliminary analyses suggest that much of the freshened water could be tens of thousands of years old, likely deposited when glaciers retreated from New England. That means it may not be getting replenished by rainfall today, making it a finite resource — though some portions could still be slowly recharging. At the same time, mapping the aquifer’s volume and chemistry gives scientists a baseline: if people or ecosystems ever need to tap into it, they’ll know what’s there, how it flows, and how to manage it sustainably. “We’re just trying to understand the science of how the water got there, and then we can put it in models and try to predict how it’s going to evolve in New England over the next 10 years, 50 years, 10,000 years,” Dugan said.
Before any of that water could theoretically be extracted, extensive political, management, and environmental discussions would have to take place. Dugan and his team wouldn’t be involved in that, but he said they would provide guidance based on their research.
So how much water are we talking about? While teams are still analyzing data and can’t quantify it precisely, preliminary calculations even before Dugan’s team drilled suggested that if you added up all the water between Long Island and Nantucket, there would be enough to supply New York City for 800 years.
“We’re not saying New York City gets it, but just to put it in a frame of context, that’s how much water we’re talking about — not a small volume,” Dugan said. “And our initial results indicate that [we’re] probably not too far off.”
The big question, he says, is whether all the water was deposited 30,000 years ago, making it a finite resource, or if it’s still being recharged today — whether “the rainfall that happens in the next nor’easter is seeping into the ground and making its way offshore.”
Dugan says that preliminary research suggests that the water is likely tens of thousands of years old. “If you think about the geology for Cape Cod, Martha’s Vineyard, Nantucket, Long Island — ten to twenty thousand years ago, it was a heavily glaciated margin, so those large glaciers were probably a very significant contributor to how all this water got into the ground,” Dugan said.
And how might this water be extracted?
The process, Dugan says, would look quite a bit different from the vertical drilling his team used to collect samples. Accessing the aquifer would likely require directional or horizontal drilling from land or offshore platforms, similar to techniques used in oil and gas development.
Think about going to the beach and digging a hole and it fills with water. What does that water look like that was in those pores between those sediments?
– Brandon Dugan, co-chief scientist of the International Ocean Drilling Programme
Moreover, just because something is technically possible doesn’t mean it’s simple or advisable. To begin with, pumping water from beneath the seafloor could alter pressure in the sediments, potentially changing how freshwater and saltwater interact.
There would also be significant environmental, regulatory, and energy considerations, including questions about impacts to marine ecosystems and complex permitting processes involving state and federal agencies. And drilling, pumping, transporting, and treating the water would all require infrastructure, money, and power.
Dugan notes that New England’s offshore wind farms represent a potential energy source if extraction were ever considered. “But before any of that could happen, we’d have to figure out who’s going to manage this water, who owns this water, and who has the rights to distribute it. And we don’t know the answers to those things yet.”
But first, he says, scientists need to understand the system. Only then could policymakers, management firms, and government agencies begin thinking seriously about whether and how to use it.
“I think 10 years is not an unreasonable horizon where someone is probably going to be working with management firms and lawyers and government agencies to try and actually produce some of this water,” Dugan said, whether for immediate use or as a future emergency supply.
Even the scientific drilling required extensive oversight. The team worked with the Department of State and federal agencies including NOAA Marine Fisheries and the EPA to evaluate noise, discharge, and potential environmental impacts.
Dugan also met with communities on Nantucket and Martha’s Vineyard before the expedition. Some residents raised concerns, particularly in the wake of the 2024 wind turbine blade collapse that sent debris onto local beaches. Dugan emphasized that the drilling operation would leave no infrastructure behind. The only discharge would be recirculated, non-toxic drilling mud — material composed of naturally occurring substances.
The team also consulted with Tribal Nations, acknowledging longstanding cultural ties to water and the region’s submerged landscapes from when sea levels were lower. They established contingencies in case artifacts were discovered and agreed to halt operations if protected wildlife, including right whales, were observed.
“I love my science,” Dugan said, “but I don’t get to do it if people don’t let me work in their backyard.”
Mark Willett, director of Nantucket’s water department, said he’d been hearing about the offshore aquifer for years before the drill rig finally arrived.
“It was a long time in the making,” he told me. “COVID happened and slowed everything up, and then the group of scientists was finally able to get the rig and come over. It was really good science and really good results.”
For Willett, the findings are exciting. First, the idea that vast stores of freshwater may sit just offshore has global implications.
“The model they used to figure out this location is going to lead to multiple places around the world where they’ll be able to find the same type of situation,” he said. “There could be countries in desperate need of water, and this may be a solution.”
What’s more, Nantucket’s own water supply — drawn entirely from a sole-source aquifer beneath the island — is already under pressure.
Most of us think of water as sort of an infinite resource, but in this case, likely because we're surrounded and encapsulated by an ocean, it's somewhat of a finite resource.
– Brandon Dugan
After several dry years, the island recently reached a Level 3 drought before improving slightly to Level 2 (see our story on Nantucket’s aquifer and the drought situation.) “Last summer, I don’t think it rained for two and a half, three months,” Willett said. Nantucket typically receives about 40 inches of rain annually, but in recent years that number has fallen by nearly a half.
Even so, Willett emphasized that the island isn’t in immediate danger of running out of water. “The drought condition isn’t so much that we’re going to run out,” he said. “It’s how to manage the resource to make sure the aquifer stays healthy long enough to get out of the drought.”
That balance depends on recharge, and not all precipitation makes it back underground. Roughly half of rainfall is lost to evaporation and plant use before it can seep into the aquifer, Willett said. And snow contributes less than people might expect.
Still, Nantucket’s aquifer remains relatively stable. “We keep an eye on it. We have a pretty good supply of water,” he said. “But it wouldn’t break my heart if we had access to all that water offshore.”
That being said, he acknowledges that “The expense to get it from 35 or 40 miles offshore to here — that’s not cheap. You’d need pumps and pipelines, or tankers to bring it in … It would be pretty costly.” And then there are the unresolved questions about ownership. “It’s like any other resource in international waters,” Willett said. “I don’t know the legality of trying to claim that water source.” He worries that, without clear regulation, private companies could attempt to extract and commercialize it. “People are paying six or seven bucks for Fiji water — what do you pay for ancient glacial water that’s 25,000 years old?”
There’s also the possibility, still under investigation, that the offshore aquifer could be connected to the island’s own (and potentially Martha’s Vineyard’s) groundwater system. Scientists are analyzing chemical signatures and isotope ratios to determine whether the sources are linked.
If they are, Willett noted, the water could fall under state jurisdiction. “The Commonwealth of Massachusetts owns the water resource,” he said. “We don’t own it — we just use it. And the Commonwealth tells us how we can use it.”
For now, like Dugan, Willett is waiting on the data. “I’m just excited to hear back from the team,” he said. “To find out what they found and what it is.”
What You Can Do: Water Conservation Tips
With Nantucket experiencing Level 2 drought after several unusually dry years, water conservation is top of mind for local officials. While the island’s aquifer remains stable, managing demand is critical, especially heading into the summer season.
“If everybody just helps a little bit,” said Mark Willett, director of Nantucket’s water department, “it’ll get us through this drought situation.”
Focus on outdoor water use
“Irrigation is going to be a big one,” Willett said. Limiting lawn watering, or skipping it all together, can significantly reduce overall demand. Get a rain barrel and use that water for outdoor uses.
Be mindful indoors
Shorter showers, running full loads of laundry and dishes (better to do them in the dishwasher than by hand), and turning off the tap while brushing your teeth all add up. “Even if people just cut back a little bit … that makes a huge difference,” Willett said.
Understand where water comes from
“All the water you’re using is coming from the aquifer,” Willett said. “Just be mindful when you turn the tap on.”
And remember that only about half of rainfall actually makes it down to recharge the aquifer; the rest is lost to evaporation and plant use. Snow contributes less than it appears to. “When you get 10 inches of snow, that’s really only about one inch of rain — so it’s really only half an inch that makes it down to the aquifer.”
