The world’s freshwater is getting saltier. Why?

Summary

Podcast Summary: Short Wave

Episode: The world’s freshwater is getting saltier. Why?
Date: March 25, 2026
Host: Emily Kwong
Producer/Reporter: Burley McCoy
Guests: Hilary Dugan (Freshwater Scientist), Kyung Do “Do” Han (Groundwater Postdoc), Allison Madison (Saltwise Nonprofit), Brian Vogt (Contractor)

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Overview

This Short Wave episode delves into the surprising and growing issue of freshwater sources—lakes, rivers, and groundwater—becoming saltier worldwide. Through a trip to Madison, Wisconsin, host Emily Kwong and producer Burley McCoy investigate how road salt and other human activities are altering the chemistry of water we depend on. They explore the environmental, ecological, and human health consequences, spotlight innovative solutions, and discuss the challenges of “desalting” our freshwater future—all in Short Wave’s trademark mix of clarity, curiosity, and humor.

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Key Discussion Points & Insights

Why Is Freshwater Getting Saltier?

• Major Contributors:
  • Road Salt: Millions of tons used in snowy regions wash into lakes and rivers during winter.
    • “Here in the Midwest, we're, you know, putting millions of tons of road salt into the environment every winter.” – Hilary Dugan [01:16]
  • Other Causes: Runoff from fertilizers, mining activities, and seawater intrusion—especially when aquifers are over-pumped and ocean water seeps in [05:14].
  • Climate Change: As temperatures rise, more water evaporates, concentrating the existing salt [05:36].

Madison, Wisconsin: A Case Study

• Local Impact:
  • Madison’s lakes had little salt before road salt usage. Now, Lake Wingra is at over 100 mg/L, nearing tastes detectable to people [04:44].
  • Broader Scope: In 2017, half of hundreds of surveyed lakes in the northern US and Canada showed increasing salinity [04:50].
• Quote:
  • “Before road salt was introduced, the lakes around Madison had virtually no salt. Today…at over 100 milligrams per liter.” – Burley McCoy [04:29]

Environmental Impact

• Toxicity: Even minor salinity changes harm aquatic plants and animals; existing levels in Madison’s lakes are toxic for fish, snails, and zooplankton [05:54].
• Invasive Species: They often thrive in higher salinity, potentially displacing native species [06:17].
• Subtle Harm:
  • “Even if you're not dying, you still might be stressed by that high salinity…you're not gonna necessarily die, but…you're not gonna feel good, and it might be affecting other parts of your health.” – Hilary Dugan [06:35]

Salinity and Human Health

• Drinking Water: Elevated salt is appearing in some municipal wells, not just lakes [07:02].
  • “Yikes. Okay, one well… Well 14 passed 120 milligrams per liter in 2014…not bad for you, unless you're on a low sodium diet.” – Emily Kwong & Burley McCoy [07:32]
  • “People have documented rising chloride levels in wells across the U.S.…in rural places and urban places.” – Burley McCoy [07:37]
• Chloride Persistence:
  • “Chloride is a persistent chemical, persistent substance that doesn't go away easily…We're still getting the legacy of salt used from 1970s and 1980s.” – Kyung Do Han [08:56]

Challenges of Removal

• Desalination is Costly:
  • “To get the salt out of the water, you gotta boil it…or use reverse osmosis. And both are really expensive and require a lot of energy.” – Kyung Do Han [08:14]

Societal Impacts

• Some communities must buy bottled water because groundwater is too salty, even impacting farmers (like forcing a family to sell dairy cows) [09:16].

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Solutions & Innovation

Saltwise & Reducing Road Salt

• Nonprofit Advocacy:
  • Saltwise leads education and training to curb salt use—removing excess, calibrating equipment, measuring pavement temperature, and advocating for alternatives [09:42].
  • “I think of it as kind of being a cheerleader for using less salt.” – Allison Madison [09:56]

Brining the Roads

• Liquid Brine Application: Spraying brine before storms keeps salt in place and prevents snow from bonding to pavement [10:24].
• Quote:
  • “If we can prevent the bond from forming between the snow and the pavement, it takes a lot less salt on the back end.” – Allison Madison [10:53]

Grassroots Engineering

• Contractor DIY:
  • Brian Vogt built his own brine truck and homemade brine maker; he now uses substantially less salt for snow removal [11:28].
  • “Once you figure this out, the liquid, you can get it done with way less salt.” – Brian Vogt [12:21]
  • “The properties that I do and I service don't look like those properties that have…you're tripping on salt.” – Brian Vogt [12:11]

Is It Enough?

• Major Reductions:
  • Madison has dropped salt use by about 40% [12:44].
• Tough Tradeoffs:
  • “If I was going to tell people we need to stop using salt, I would be laughed out of the room…But from an environmental perspective, yes, we should stop using salt today.” – Allison Madison [12:51]

Broader Reflections

• Lasting takeaway: Solutions are both simple (stop adding salt) and hard (changing long-standing habits and expectations). But persistent, community-level efforts can make a significant impact [13:11].

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Notable Quotes & Memorable Moments

• “We're now talking 70 plus years of road salt use. And what we've seen in the lakes is the salinity kind of steadily increasing year after year as more and more salt is put down.”
  – Hilary Dugan [01:32]

• “Chloride is a persistent chemical…those are still affecting our lives, present day.”
  – Kyung Do Han [08:56]

• “The obvious way to slow or stop water from getting saltier is to use less salt.”
  – Burley McCoy [09:38]

• “Once you figure this out, the liquid, you can get it done with way less salt.”
  – Brian Vogt [12:21]

• “If I was going to tell people we need to stop using salt, I would be laughed out of the room. Right? But from an environmental perspective, yes, we should stop using salt today.”
  – Allison Madison [12:51]

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Timeline & Timestamps

• [00:31] – Introduction to freshwater salinization as an emerging global threat
• [01:16] – Hilary Dugan explains decades of road salt use and environmental build-up
• [04:44] – How salinity in Madison’s lakes has risen since road salt was introduced
• [05:07]–[05:46] – Other sources: run-off, mining, seawater intrusion, climate change
• [05:54]–[06:35] – Ecological impacts and example of species stress/death
• [07:02]–[08:02] – Salinity entering human drinking water and health guidelines
• [08:05]–[08:56] – Difficulty of filtering/removing salt; historical persistence
• [09:38]–[10:53] – Advocacy for less salt, industry education, and technological solutions (brine)
• [11:02]–[12:21] – Grassroots innovation with brine trucks and their effectiveness
• [12:44]–[13:11] – Evaluating if these efforts are enough; practical constraints

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Takeaway

Freshwater salinization is a creeping yet under-appreciated environmental crisis, driven by common practices like road salting and exacerbated by climate change. While challenging to reverse, meaningful progress is possible through smart policies, technical innovations, and community engagement. The episode illustrates how environmental solutions, though not easy, can succeed piece by piece—and that everyone, from scientists to snowplow drivers, has a role in protecting water’s delicate balance.

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Transcript

[A]

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[B]

You're listening to Short Wave from NPR. Hey, Shortwavers. Emily Kwong here. And this week we are doing a deep dive into a vital resource that all of life depends on, water with producer Burley McCoy. Hey, Burley.

[C]

Hey, Emily. So, okay, today I want to talk about a phenomenon that's happening all over the world to fresh water. So we're talking lakes, rivers, groundwater, they are all getting saltier.

[B]

Wait, what? Why is fresh water getting saltier?

[C]

Well, it's for a few reasons, but to figure out why, I recently took a trip to Madison, Wisconsin. And there it's mainly because of all the road salt they put down in the colder months to melt snow and ice. Wow.

[D]

So here in the Midwest, we're, you know, putting millions of tons of road salt into the environment every winter.

[C]

This is Hilary Dugan. She studies freshwater at the University of Wisconsin, Madison. And she says the road salt eventually washes away and ends up in the local water.

[D]

We're now talking 70 plus years of road salt use. And what we've seen in the lakes is the salinity kind of steadily increasing year after year as more and more salt is put down.

[B]

I guess it really does add up.

[E]

Yeah.

[B]

That much road salt and it's really impacting the environment.

[C]

Yeah. And the drinking water where it's also starting to show up. And this is not just Madison's water. Freshwater is getting saltier all over the world for a lot of reasons beyond road salt. And it's a problem scientists have just started seriously studying in the last few decades.

[B]

Today on the show, what happens when Earth's fresh water gets too salty?

[C]

And is there anything we can do about it?

[B]

You're listening to Shortwave, the science podcast from NPR Foreign.

[A]

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[B]

so you took a trip to Madison, Wisconsin to report on this global phenomenon of freshwater getting saltier. So what makes Madison a good place to look into this?

[C]

Well, water is a big part of life there. There are these two big lakes on either side of downtown. The university campus is right on the shore of one of them. In the summer, there's a waterfront festival. In the winter, there's a festival on frozen lake ice. You just get the that the lakes are a part of life there. So it wasn't a good thing when a few decades ago, people started noticing the salt levels or the salinity of the local lakes were really rising. Before road salt was introduced, the lakes around Madison had virtually no salt. Today, the saltiest lake in Madison is Lake wingra at over 100 milligrams per liter. So it's still technically considered fresh water, but that level is approaching the point that some people could start to taste it in water.

[B]

That is a huge change. And you said it's happening all over the world, not just in Madison?

[C]

Yeah, lots of places. In 2017, Hillary looked at hundreds of lakes in the northern US and Canada and found that around half of them had gotten saltier. Basically, if a lake is by a road that's salted, it's super likely some of that salt is going to end up in the lake. And that's the case globally as well.

[B]

Is road salt the only reason that water around the world is getting saltier? There has to be other stuff.

[C]

Yeah, so in places where it snows a lot, it is often because of road salt. But salt can come from runoff, from fertilizer or mining activities. And another big source is something called seawater intrusion.

[B]

Oh, yeah, we talked about that in yesterday's episode. And how one way this happens is when people pump too much water out of their local aquifer and ocean water starts flowing in.

[C]

And, Emily, then there's climate change. So as global temperatures go up, more freshwater evaporates, which makes things saltier because you have less water but the same amount of salt.

[B]

So I'm hearing there's lots of reasons that the world's fresh water is steadily becoming more salty. What is the overall impact then on the environment?

[C]

Well, when there's more salt than there should be in the environment, it basically acts as pollution. It's affecting plants and animals, and even small changes in the salt levels can lead to death. So salt at the levels that are in Madison's Lake Wingra right now have been shown to be toxic to fish and snails and zooplankton. The exception to all this are often invasive species. So those are the ones that are more adaptable to new environments, hence why they're invasive. So more salt could actually mean you're giving invasive species more room to thrive over native ones. Oh, yeah. Wow. So Hilary Dugan, the freshwater researcher we heard from earlier, also points out that for, say, a fish or a plant,

[D]

even if you're not dying, you still might be stressed by that high salinity. Like, think about humans. If you drink or eat too much salt, like, you're not gonna necessarily die, but, like, you're not gonna feel good, and it might be affecting other parts of your health.

[B]

I don't know what she's talking about. I feel great when I chug a bunch of salt water. And is this salinity impacting creatures beyond fish and snails? I mean, is it getting into human drinking water?

[C]

Yeah, it is.

[B]

What's the effect there?

[C]

So road salt is usually made out of sodium chloride. And. And the American heart association recommends 2,300 milligrams of sodium a day as the max that a human should intake, but says actually, you should probably keep it under 1500 milligrams per day. That's ideal. Okay, so now, in Madison, the drinking water comes from wells, not from lakes. But the city officials have measured increasing salt levels in some wells, too.

[B]

Yikes.

[C]

Okay, one well. Well, 14 passed 120 milligrams per liter in 2014, which. Okay, still probably isn't bad for you, unless you're on a low sodium diet, then that amount can add up if you're drinking a few liters a day. Because people also get salt from their food. And people have documented rising chloride levels in Wells across the U.S. michigan, New Jersey, Idaho, Arizona. These are in rural places and urban places.

[B]

Can't the local water plant just filter the salt out?

[C]

So I talked to Kyung Do Han about this. He goes by Dough. He's a postdoc at the University of Wisconsin, Madison, studying groundwater. And he says you can filter it

[F]

out, but it is extremely expensive. So to get the salt out of the water, you gotta boil it to get the distilled water or you gotta use reverse osmosis. And both are really expensive and requires a lot of energy.

[C]

Do told me he got into the field because when he was a kid, his family's local water source was contaminated by a nearby military base in Korea. It started causing health issues for his family, and he remembers having rashes and sometimes vomiting until they moved and the issues went away.

[B]

So he's really passionate about keeping drinking water clean.

[C]

He is. And he's aware of how big the problem is in Madison because chloride is

[F]

a persistent chemical, persistent substance that doesn't go away easily. So we are still getting the legacy of salt used from 1970s and 1980s. Those are still affecting our lives, present day lives.

[B]

This is making me realize how long salt sticks around.

[C]

Yeah. I mean, one of my sources told me that some people in New York have to buy bottled water because their groundwater is too salty to drink. And one family even had to sell their dairy cows. You can buy bottled water for your family, but you can't really buy it for your cows. So the obvious way to slow or stop water from getting saltier is to use less salt.

[B]

You can't reverse it, but you can stop it from getting worse, from getting saltier.

[C]

Right. And one person who is advocating for this is Allison Madison. She leads a nonprofit called saltwise, which started when people at the city and county levels in Madison started noticing salt levels going up in drinking water and wastewater.

[E]

I think of it as kind of being a cheerleader for using less salt.

[C]

So saltwise leads trainings and talks. They advocate for things like cleaning up extra salt before it washes away or calibrating equipment. So plow drivers know how much their salt trucks are putting down.

[E]

Yeah.

[C]

Which changes with the pavement temperature. So people should also be measuring that. And something that has made a big difference in using less salt is liquid brine. What?

[B]

Brining the roads. Brining the roads like brined turkey for Thanksgiving?

[C]

The very same. Emily. What? So the city now sprays streets when a storm is predicted before the snow falls.

[E]

Because you can actually lose 30% of your salt off the road as the truck drives by. So that spraying it with brine helps it stay in place. It sticks and it starts working faster.

[C]

So Allison says it makes it so snow doesn't stick easily to the pavement. So think of cooking without oil in your pan. Food's going to stick.

[E]

The same thing is true on our pavement. If we can prevent the bond from forming between the snow and the pavement, it takes a lot less salt on the back end.

[C]

So one person who knows about this is Brian Vogt. He's a contractor who does snow removal for small commercial businesses. And he used to use a lot of rock salt. But some years ago, he saw a YouTube video of someone building their own brine truck. He's got a mechanical engineer background and likes a challenge.

[G]

So it sounded like a good idea to me. I just started experimenting a little.

[C]

And then he decided to build his own truck.

[B]

His own brine truck.

[C]

His own brine truck.

[G]

The Honda gas pump engine. Bigger flow valves, like 2 inch. And then basically it's a three lane system. Calculated flow too.

[C]

So like these and Emily, I got to see this truck. It's essentially a plow truck with a tank and a motor in the back of the truck that sprays brine out of a bar by his bumper. He even makes his own brine at his rural property.

[G]

My redneck homemade brine maker.

[C]

And he has a walk behind sidewalk version.

[B]

It's like his own R2D2, that's brace brine.

[G]

So you would do two passes on a sidewalk there and back, and you're done.

[C]

Brian says he wasn't even really thinking about the environment, but that seeing excess salt on the ground is a pet peeve of his.

[G]

The properties that I do and I service don't look like those properties that have. You're tripping on salt.

[C]

And he says he's noticed a difference.

[G]

Once you figure this out, the liquid, you can get it done with way less salt.

[B]

I love this person. Just the recognition of a problem, but the innovation to do something about it.

[H]

Yeah.

[C]

And Allison says it's solutions like these community based grassroots that can make a big difference in keeping salt out of freshwater. She told me that the city of Madison has dropped their Salt use roughly 40%.

[B]

Forty percent's good. Is it enough though? Because even with everyone using less salt, they're still using salt.

[C]

So this is what she told me.

[E]

If I was going to tell people we need to stop using salt, I would be laughed out of the room. Right? So I kind of have to meet people where they're at and have them know that I understand the realities of their jobs and kind of resident expectations. But from an environmental perspective, yes, we should stop using salt today.

[C]

And that's true. Whether it's road salt or salt from mining or fertilizer, the solution is both simple and hard. Stop adding salt to the environment. Right? And that was eye opening for me. I grew up in the Midwest and I got used to seeing salt everywhere. I'd never thought about where it went and it's a tough sell in ice prone areas, but a lot of places like Madison have gotten really serious about at least pulling back their salt use. This story reminded me how solutions can happen if enough people get on board.

[B]

Burleigh McCoy, thank you so much for this story.

[C]

You're welcome.

[B]

If you liked this episode of Short Wave, please share it with a friend because it really helps our show out. And check out all the episodes in our Water series. This episode was produced by Hannachin. It was edited by our showrunner, Rebecca Ramirez. Aru Nair checked the facts. Jimmy Keeley was the audio engineer here. I'm Emily Kwong. Thanks for listening to Short Wave, the science podcast from npr.

[H]

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