Short Wave - The world’s freshwater is getting saltier. Why?

Episode Date: March 25, 2026

Around the world, the planet’s freshwater is getting saltier. And it’s because of people. For decades, salting roads, fertilizer run-off and evaporation driven by human-caused climate change have upped the salinity of lakes, rivers and groundwater. All that salt is detrimental to a lot of aquatic life and can be problematic for drinking water, too. But there’s still time to reverse course. In fact, many people have already started to change their ways. Today, producer Berly McCoy is on the case to see what solutions exist. This is part of a whole series on the world’s dwindling water supply. Check out the rest of the water series:Part 1: When the wells run dryPart 2: The world’s groundwater problemPart 3: Freshwater’s growing salt problemEmail us your questions about water, the wider environment – or anything else to do with science at [e-mail]. We may turn it into an episode in the future!Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave.See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave 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. Hey, Emily. So, okay, today I want to talk about a phenomenon that's happening all over the world to freshwater. So we're talking lakes, rivers, groundwater. They are all getting saltier. Wait, what?

Why is freshwater getting saltier? 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. So here in the Midwest, we're putting millions of tons of road salt into the environment every winter. This is Hillary Dugan. She studies freshwater at the University of Wisconsin-Madison, and she says the road salt eventually washes away and ends up. up in the local water.

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. I guess it really does add up. Yeah, that much road salt. And it's really impacting the environment. 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. Today on the show, what happens when Earth's freshwater gets too salty? And is there anything we can do about it? You're listening to Shortwave, the science podcast from NPR. Okay, Burley, 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? 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 feel 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 freshwater, but that level is approaching the point that some people could start to taste it in water. That is a huge change. And you said it's happening all over the world, not just in Madison. Yeah, lots of places. In 2017, Hillary looked at hundreds of lakes in the northern U.S. in 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. Is road salt the only reason that water around the world is getting saltier?

There has to be other stuff. 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. Oh, yeah. We talked about that in yesterday's episode. 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. 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. So I'm hearing there's lots of reasons that the world's freshwater is steadily becoming more salty. What is the overall impact then on the environment? 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 nature. ones. Oh. Yeah. Wow. So Hillary Dugan, the freshwater researcher we heard from earlier, also points out that for, say, a fish or a plant. 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 going to necessarily die, but like, you're not going to feel good. And it might be affecting other parts of your health. 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?

Yeah, it is. What's the effect there? So Roadsalt is usually made out of sodium chloride, and the American Heart Association recommends recommends recommends a day as the max that a human should intake, but says, actually, you should probably keep it under 1,500 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. Yikes. 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. Can't the local water plant just filter the salt out? So I talked to Kyeongduhan about this. He goes by Do.

He's a postdoc at the University of Wisconsin-Madison studying groundwater. And he says you can filter it out, but... It is extremely expensive. So to get the salt out of the water, you've got to boil it to get the distilled water, or you've got to use reverse osmosis. And both are really expensive and requires a lot of energy. Doe 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.

So he's really passionate about keeping drinking water clean. He is, and he's aware of how big the problem is in Madison. Because chloride is 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. This is making me realize how long salt sticks around. Yeah. 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 because 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. You can't reverse it, but you can stop it from getting worse, from getting saltier. 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. I think of it as kind of being a cheerleader for using less salt. 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.

Yeah. 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? Brining the roads? Brining the roads. Like you brined a turkey for Thanksgiving?

The very same, Emily. What? So the city now sprays streets when a storm is predicted before the snow falls. Because you can actually lose 30% of your salt off the road as the truck drives by. So that spraying with brine helps it stay in place. It sticks. and it starts working faster. 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. 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. So one person who knows about this is Brian Vogue. 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 you. to video of someone building their own brine truck. He's got a mechanical engineer background and likes a challenge so... It sounded like a good idea to me. I just started experimenting a little and then... He decided to build his own truck.

His own brine truck. His own brine truck. It's just a Honda gas pump engine. Bigger flow valves like two inch and then basically it's a three lane system. This is all calculated flow too. So like these... And Emily, I got to see this truck. It's essentially a plow truck with a tank

in a motor in the back of the truck that sprays brine out of a bar by his bumper. He even makes his own brine and his rural property. My redneck homemade brine maker. And he has a walk behind sidewalk version. It's like his own R2B2 that sprays brine. So you would do two passes on a sidewalk there and back and you're done. 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.

The properties that I do and I service don't look like those properties that have your tripping on salt. And he says he's noticed a difference. Once you figure this out, the liquid, you can get it done with way less salt. I love this person. Just the recognition of a problem, but the innovation to do something about it. Yeah, 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%.

40%'s good. Is it enough, though? Because even with everyone using less salt, they're still using salt. So this is what she told me. 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.

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. Burley McCoy, thank you so much for this story. You're welcome. If you liked this episode of Shortwave, 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 Hannah Chin. It was edited by our showrunner, Rebecca Ramirez. Arru Nyar checked the facts. Jimmy Keely was the audio engineer.

I'm Emily Kwong. Thanks for listening to Shortwave, the science podcast from NPR.