by Dan Weissmann, originally published on February 10, 2015

Greater Miami is a place where the idea of not having enough water seems completely bananas. South Florida receives about 60 inches of rainfall a year, and groundwater is more than plentiful. Keeping streets and homes from getting flooded with freshwater is still a huge job here.

But rising sea levels change things in unexpected ways, and seawater threatens to turn the drinking water salty. In some places, the ocean has already made good on that threat. And the problem is going to get worse.

To illustrate, Harold Wanless takes me out behind a car-rental place by the Miami airport. He’s a University of Miami geology professor who has spent decades studying how sea levels change, from the ice ages to today.

There’s a lot to see and hear in this little spot: two highways converging, planes flying overhead, Miami Jai-Alai, the Pink Pussycat Strip Club. (“Everything you want near an airport,” says Wanless. “I guess.”)

He’s chosen this location for two reasons. First, this entire area used to be part of the Everglades. “When they drained the Everglades here, water levels dropped about 7 feet,” he says. “And voila! You have an airport.”

Second, in this particular spot, a canal comes under those highways and hits a little barrier. This structure, several miles inland, is the boundary between the salty ocean water, and South Florida’s freshwater supply.

That water supply isn’t contained underground. “It goes right up to the surface,” says Wanless. “So, yeah – this is our aquifer. This is our water.”

And this is where the goal of managing freshwater flooding meets the threat of rising seas.

One of this little barrier’s main jobs is actually to get rid of freshwater after heavy rains, to prevent flooding. The gate opens and rainwater building up behind the dam spills out to sea.

There are dams like this all over the region. But for them to work – for the freshwater to spill – the seawater has to be lower than the gate.

Which it won’t be for much longer. “By the middle of the century, or before, 82 percent of these structures will no longer function,” Wanless says.

Meaning, if those gates got opened, seawater would flow in. And salt would contaminate the drinking-water supply.

Keeping the gate closed would mean flooding out areas on the freshwater side.

Miami Beach is spending up to $400 million on pumps to send floodwater out to sea.

But there’s another threat to drinking water, underground. And it’s already resulted in contaminated drinking-water wells in some cities here.

To see that threat, I went to West Palm Beach – the offices of the South Florida Water Management District – to meet Jayantha Obeysekera, a scientist there with the title chief modeler of hydrologic and environmental systems.

Essentially, he looks at the big picture, and he showed me what’s under South Florida. “This is a little prop that I use,” he says, pulling a piece of rock out of wrapping paper.

It’s called porous limestone. Before I got here, I was thinking, porous like a membrane – maybe a really thick, hard coffee filter? But no.

“This is like Swiss cheese,” says Obeysekera. “There are a lot of openings for water to move through.”

He’s understating things. Swiss cheese doesn’t have this many holes. This is all openings. It’s porous like a volleyball net.

And this is what makes South Florida’s problem with rising seas, well, special.

“People suggest, why don’t we do what the Dutch do,” says Obeysekera. “Build a levee and stop the seawater coming,”

With rock like this, that won’t work. A levee, says Obeysekera, “may stop the seawater storm surge on the surface, but the water will come underground.”

That’s what’s happening right now. And before seawater floods the land, it’s flowing into the water supply.

To describe that process, it will probably help if we first clear up a question: If there’s really no barrier between saltwater and fresh underground water, why isn’t all the drinking water salty already?

The reason is gravity. Saltwater is heavier than freshwater. Some seawater has always moved into the limestone, but it sits under the freshwater, which floats on top.

Then sea levels rise. Saltwater pushes up to where that freshwater was floating. It doesn’t have to push all the way to the surface to cause problems – just to the depth where the local well got sunk a few decades ago.

When that happens, “those well fields will be impacted,” says Obeysekera. “They will go salty.”

That’s already happened in parts of Broward County, north of Miami. Some municipalities there now get some of their water from a county facility farther inland.

The more sea levels rise, the farther inland the saltwater comes, and the more places get affected.

Jennifer Jurado directs Broward’s environmental planning division, which means she oversees the county’s long-term water planning. She shows me maps of where the saltwater has already come – and where it’s heading: Hollywood, Hallandale, Dania Beach, Fort Lauderdale … the list goes on.

“It’s quite significant,” says Jurado. And it’s not just Broward.

That’s why Wanless has spent almost 20 years trying to warn his neighbors across South Florida: They’d better start planning.

“If we get blindsided,” he says, “we’re a bunch of Okies.” As in: Dust Bowl refugees. No water, no viable anything. “It’s going to be ugly,” he says.

For years, his warnings got a less-than-warm reception. Then, gradually, things changed.

“It was maybe 2005 when I would give a talk to a Rotary or business group,” he says. “They stopped yelling obscenities, at the end or during the talk, and they started listening.”

A couple of years later, he says, there was another shift. “People were starting to hang around after talks,” he says. They wanted to know what they could do, what the community could do.

Now, he says, he hears from people who have helped themselves.

“It’s truly unbelievable,” he says, “the number of people that call me or send a note saying: ‘We had three or four properties. We just sold them and made a killing, and thank you so much.'”

Meaning, they’ve gotten out while property values are still high. “We’re truly entering a time of what will become real-estate roulette.”

Looking at projections on a 30-year horizon, he says – that’s as long as a mortgage.

Wanless is not alone in his thinking. I meet Rene Machado as he prepares for a round of golf in Coral Gables. He’s 75, moved here 10 years ago from New York — and he thinks Coral Gables is the best place on earth: lush, peaceful and close to downtown.

“It’s like being in New York City and living in Central Park,” he says. “How cool is that?” And, bonus: It’s never winter.

I ask if he thinks about the rising sea levels, the threat. He says, sure. All the time.

And yes, he thinks about how long he should keep owning a home here. “I would evaluate every five years,” he says. “I think after 10 years, I have to take it seriously.”

From the windows of his 24th-floor office in downtown Miami, land-use attorney Wayne Pathman has a panoramic view of Miami Beach and the central city. There are cranes everywhere, putting up new skyscrapers. Pathman has played a role in some of these projects.

However, he doesn’t think everything we see will survive the next few decades, as rising seas encroach.

“There are solutions,” he says. “Man has been very good at finding solutions. But I don’t think we’re saving everything.”

He’s been pushing for local officials to rethink building codes, to account for where sea-levels will be in a few decades.

“This is a very developed area – high-density population – and it’s coming,” he says. “And we keep building as if it’s not, and we keep living here as if it’s not.”

These new skyscrapers are just a small fraction of what he’s talking about. South Florida’s population was about 5 million in the year 2000. Now it’s almost 6 million and growing.

Defending structures against flooding, whether from storms or higher seas, seems like the most-immediate issue, but threats to the water supply can’t be ignored.

“Obviously, nobody lives here if we don’t have potable water,” Pathman says.

Not even behind a seawall.