Alison Stewart: This is All Of It on WNYC. I'm Alison Stewart. New York City's water supply is an engineering marvel. When you talk about it, you can justifiably throw around a lot of superlatives. I'm not just talking about how our tap water is often referred to as, "the champagne of drinking water." Don't take my word for it. Here's German water sommelier, Martin Riese, who made a TikTok video of a taste test. We edit out the swishing and spitting part.

Martin Riese: This water has no chlorine whatsoever. What is very, very nice. It's super refreshing. It's nice and cold like New York. I like this.

Alison Stewart: More superlatives. We have the largest municipal water supply system in the country. It brings 1 billion gallons of water each day to roughly half of the population of New York state. It's also the largest unfiltered water supply in the country. One of the tunnels that brings water from the Catskill regions to the city, the Delaware Aqueduct is 85 miles long from end to end, making it the longest tunnel in the world. That tunnel has also been leaking since 1990s. Now it's finally ready to be fixed. While that work is happening, the city must tweak how it gets its water.

If you're not noticing a slight change in taste, you are not imagining things. Joining me now to talk about all of this is Rohit Aggarwala, commissioner of New York City's Department of Environmental Protection. Commissioner, thanks for joining us.

Rohit Aggarwala: Thanks for having me, Alison. It's good to talk to you. Appreciate it.

Alison Stewart: Can you give us New York City tap water one on one? Where does it come from? Where do we get it?

Rohit Aggarwala: Well as you said, we like to think it is the champagne of drinking water. New Yorkers benefit from, in fact, 180-year-long tradition of New York City investing in a phenomenal water infrastructure. Our water comes from north of New York City, from 19 different reservoirs that we have as near as Hillview Reservoir, right on the Yonkers Bronx border, all the way up to 125 miles north of the city at Gilboa in Schoharie County. 90% of our water comes from west of the Hudson River, from the Catskills. That water, we do such a good job of protecting the area around it. We own a lot of the land up there. We actually own more land in the watershed than there is land in the five boroughs.

That protects our water so that we don't even have to filter it. It's so clean that the EPA and the New York State Department of Health don't require filtration. We do treat it, of course, there's some chlorine we put in and take out and some other things, but nonetheless, it is really a pristine water supply.

Alison Stewart: In a 2003 article about the construction of city tunnel number three, The New Yorker wrote, as an engineering feat, the water tunnel system rivals the Brooklyn Bridge and the Panama Canal. What makes it so unique?

Rohit Aggarwala: Well, it's in part the scale, it's in part the history. A number of other cities have multi-reservoir systems that carry water over long distances. Nobody has one quite as big as ours. The Delaware Aqueduct itself, at 85 miles long, is actually the longest manmade tunnel on earth. It is really one of the things that allowed New York City to grow the way it did, so much like the Brooklyn Bridge allowed the merger of the five boroughs. Effectively, the water system really is what enabled the city to grow as large as it has without having a problem and while having this amazing resource that we all benefit from every day.

Alison Stewart: Listeners, we want to hear from you. If you have any questions about the city's water supply or if you've noticed a slight difference in why it tastes the way it does, give us a call. 212-433-9692, 212-433 WNYC. You can call that number or text to us, or you can also reach out on social media @allofitwnyc. If you're a New Yorker or you travel outside the city, what do you notice about how the water tastes? Give us a call. 212-433-9692, I'm talking to Rit Aggarwala. He's commissioner of New York City's Department of Environmental Protection.

Okay, as you said, the city gets its water from the different supplies. Catskills, Delaware, the Croton. The Delaware Aqueduct is leaking. How are leaks discovered? How big are the leaks?

Rohit Aggarwala: Well, so the tunnel is leaking, we think about 35 million gallons of water a day. As you said, by reference or by comparison, we drank about a billion, or we use about a billion gallons a day in New York City. Really, the leaks were discovered because, frankly, we started to see some wetlands emerge where there hadn't been wetlands before. The water was tested, and it clearly was based on the chemical composition. It was clearly traced to our aqueduct. That's how we first, in the late 1990s, identified that there was a leak there.

We subsequently sent submarines through, like these drones that are submarines that use visual and sonar to understand what's going on in the tunnel, and they mapped where the leaks were. Then our amazing engineers set out on this nearly 20-year effort, really 15 at full throttle, both to design a bypass, but also to make sure that our system was resilient and redundant enough that New Yorkers would have no trouble getting water. That's one of the most amazing things that we also sometimes take for granted. Most cities have one reservoir or two reservoirs. We have 19 reservoirs.

There is so much redundancy in our system that it allows us to deal with all sorts of different changes in water, or if there's a storm, it'll affect one part of our watershed differently than another. Our Bureau of Water Supply is taking samples. We take hundreds of samples every day. We actually run a total of 100,000 tests all year, 100,000 tests in a given year. Every day, based on what we are finding from this chemical analysis of our water, our folks are deciding basically which reservoirs we should be drinking from the next day to get the best tasting water.

It's often a blend. I like to think about our deputy commissioner who runs that function, Paul Rush, as New York City's chief mixologist. Because every day, New Yorkers get to drink this fine blend of water that's carefully selected.

Alison Stewart: Now, there were reports that the leaks lose up to 35 million gallons a day. Is that true?

Rohit Aggarwala: Yes.

Alison Stewart: That's a lot of water. What impact have those leaks had on the communities surrounding the watershed?

Rohit Aggarwala: We have had a couple, and we've been working very closely with the neighbors and the surrounding towns on this. We've had a couple of locations where there has been enough water coming all the way up to the surface that it's caused some issues at a couple of buildings, a couple of parking lots that have had issues with their pavement, things like that. Because New York City has a really large land footprint in the watershed, we take our responsibility as a member of the upstate community very seriously.

We've certainly been compensating some of the affected landowners. We've been helping those people whose water supply is coming from this area. One of the paradoxical or ironic things about this is that there are homeowners who drilled wells and are drinking water that it turns out was actually good New York City drinking water coming through the leak. Their wells are going to dry up, and so we've worked with the city of Newburgh and others to make sure that none of those people actually lose their water supply. Nobody's had a catastrophic impact, but as I say, we take our community responsibilities very seriously.

Alison Stewart: Let's talk to Bud from Manhattan. Hi, Bud.

Bud: Hello. Hi. How are you there? I don't have a question about water taste, but I'm amazed at the water pressure. I live in a five-story building in Manhattan, does not have a water tank on top. I have never had a problem with water pressure in my building. I live on the third floor. Similarly, I have seen fire hydrants opened up, blasting water at street level. I find it difficult to believe that that pressure is maintained by the natural gravity of water flowing down from upstate New York. There has to be some mechanical means that is used to maintain water pressure for fire hydrants and apartment buildings under five stories that don't have water tanks.

Alison Stewart: I'm going to dive in right there. Is that a question you can answer?

Rohit Aggarwala: Yes, I'm happy to, but I'm glad to hear that you don't have a water pressure problem, but I will tell you that is gravity. If you look back in the history, one of the key reasons that New York City, the common Council at the time, decided to invest in what is now our water system was because there was a fire in 1835 that decimated Wall Street and a number of parts of lower Manhattan, and they couldn't put it out because the local water supplies from wells didn't have enough pressure.

One of the amazing things about this system is that it was designed, just like the water supply of, say, ancient Rome, to work on gravity. What is designed into the system is that our reservoirs up in the Catskills are at several hundred feet of altitude over sea level. Because water always seeks its own level, the pressure really is maintained through the whole system down to Hillview Reservoir, which if you drive up the Deegan Expressway and cross into Yonkers, you see Hillview Reservoir. It's at an elevation, and it's designed that way because that way the water pressure coming into the city is pressurized so that water at Hillview Reservoir is above your roof in your five or six-story building in Manhattan.

That was really designed into the system going all the way back to 1840 or so.

Alison Stewart: My guest is Rit Aggarwala, commissioner of the New York City Department of Environmental Protection. We're talking about New York City water. We'll have more after a break. This is All Of It. You are listening to All Of It on WNYC. I'm Alison Stewart. My guest is Rit Aggarwala, commissioner of New York City's Department of Environmental Protection. We're talking about repairs on the leaky aqueduct is causing New York City to have a temporary change in where it gets its drinking water.

During the maintenance, the city will be leaning more on the Croton and Catskill water supplies to make up for the shortfall while you're doing the repairs. What environmental factors make that water supply different from the water that we're used to drinking from the Delaware watershed?

Rohit Aggarwala: As I said, we're often drinking a blend of multiple reservoirs, and the reality is that any reservoir has a certain flavor. It has the soils around it, the kind of vegetation around it, et cetera. All of that is going to shape what goes into the water. It doesn't mean it's pollution. Just like if you buy a bottle of fancy mineral water, whether it's Pellegrino or Perrier, it'll list what the different alkalines and trace elements are. That's what gives spring water or mineral water its flavor. You could tell the difference between Perrier and Pellegrino when you drink it.

In the same way, the soils around our different reservoirs will shape how it tastes. The Catskills are notable for their clay soils. The Western Catskills have a slightly different composition. They don't have as much clay. That leads to a change in taste. East of the Hudson, we do have more development around our reservoirs, so that part of our system, the Croton system, does go through a set of charcoal filters at our Croton filtration plant in the Bronx. That removes a lot of the things that might taste different, but as I say, it is a bit of a change.

We put out this news a couple of weeks ago, really, just to make sure nobody noticed it and got worried, because, again, there's no change in safety. The water is just as healthy as it's always been, just as safe as it's always been, but because we're not blending in a couple of the reservoirs that we usually use, the blend might taste different.

Alison Stewart: This is a text we got. My name is Tammy, and I had a quick story. My grandmother grew up in New York City, and when she was in her 90s, she was living in Florida in a nursing home. When I would visit her to entice her to drink her water, we would tell her, it's New York water. It was magic. She would take a nice big gulp, smack her lips, and say, ah. That's a good question. We've got a question from Stephen from Irma. Stephen, go for it.

Stephen: Hey. Hi, Alison, you're a gem. Commissioner, maybe you could comment about, since all this testing is being done, about the PFAS in the New York City water supply because I know Veolia is our water company and they're monitoring that and we get notices about it because they've detected that in the water supply. The whole safe level of that is still, I think, questionable and being determined. Maybe you could comment, please, on the amount of forever plastics that are showing up in the water supply that you're aware of. Thank you very much.

Rohit Aggarwala: Yes, I'm happy to talk about that. What is called PFAS, or PFOA, which are two classes of what are often called these forever chemicals because they don't break down naturally and they're widely used in a number of household products and other things. That's a big concern to the entire water industry across the United States and around the world. The good news for us in New York is that, again, because our water comes from these areas with a lot of protections, a lot of publicly owned land, we work very closely with the surrounding communities to protect our water supplies from runoff, from anything that might come from septic tanks or anything like that. We're protecting it.

We have never had a sample where we've found PFAS at a measurable level in the New York City drinking water west of Hudson. That's a big benefit. We've identified one or two places of concern, but only on the filtered part of the system, and we are very much working to make sure we are well ahead of that risk. I'm quite content, are quite confident that PFAs and PFOA are not a concern. We are, of course, keeping up with the state-of-the-art testing. This is an evolving field, so whenever there are new tests that might be even more precise, we're certainly going to be on the lookout.

Alison Stewart: Part of the story of New York City's water involves multiple counties and requires a partnership of the agricultural sector in that area. We're getting a lot of calls and a lot of texts about fertilizer. Fertilizer and the water. Your comments?

Rohit Aggarwala: Well, yes, you're totally right. The Catskills are a traditional agricultural area, one of the key areas of New York state's dairy industry going back into the 19th century. In 1997, when there was a memorandum of understanding and an agreement called the Filtration Avoidance Determination, that's an agreement with the New York State Department of Health that allows us not to filter the water from west of Hudson. That required New York City to create a number of programs in the watershed, one of which, through grants that we give to a local organization called the Watershed Agricultural Council gives grants to farmers to adopt best management practices that control the runoff from their farms, or to help them, and sometimes fund them to adopt good fertilizing practices that do not lead to runoff.

Those issues of fertilizer runoff or animal waste runoff, our programs with the WAC have over 20 years, or more than 20 years now, really managed down to a point where we're reasonably safe. We have to keep those programs going. Just only a few months ago, I was upstate and visited with some members of the Watershed Agricultural Council. That is how we do it, and it is through these voluntary cooperative efforts with the farmers.

Alison Stewart: Let's take one more call. Gabrielle is calling in from the Lower East Side. Gabrielle, you've got about a minute?

Gabrielle: Yes, yes, yes, I'm here. Oh, should I speak now?

Alison Stewart: Yes. Actually, you know what? Because we're going to run out of time, I'm afraid. My concern is. I'm going to say what her question was. Her water is suddenly black. Comes out of her system black. It sort of jets out in a gross way, and then it goes away. When people have systems where their water is coming out dark or gray or it's gross. Is that the building? Is that you guys, the water supply? What's the deal?

Rohit Aggarwala: Well, every now and then, there are discoloration events that happen in our water system. Sometimes some sediment can build up in our water mains, even though our water is so clean. If there's construction going on or if a fire hydrant is opened and then shut off very quickly, sometimes that can be dislodged. Usually, it's not black because it's a safe iron oxide. A little bit, basically dissolved rust in small amounts that can get into your water, and that will flush its way out, and it's harmless.

It might be unpleasant to look at and drink, but it's harmless. If it's black, that's much more concerning, and that is almost certainly going to be something in the building. I would certainly talk to your building management about what might be going on. Whenever we get a call about that, we go out and we test the water at the water main nearest the building or at the fire hydrant nearest the building, which is good drinking water. Almost never do we find that that kind of discoloration is in the water main.

Alison Stewart: How long will the work on the Delaware Aqueduct take?

Rohit Aggarwala: It's roughly half a year, so we're hoping to be done sometime in the spring.

Alison Stewart: Is there a reason why-- It's not scientific, but how much truth there is to the fact that our bagels are better in New York? The water is better. Is it better? Is it better?

Rohit Aggarwala: Well, look, I'm not going to dispel a myth that serves us very well. There are a lot of reasons that pizza and bagels in New York taste better. I'm the DEP commissioner. I'm sticking to the story that the water is why.

Alison Stewart: You're not going to agree with me on that one?

Rohit Aggarwala: It's definitely the water. Of course. It's got to be the water.

Alison Stewart: Good man. Rohit Aggarwala is the commissioner of New York City's Department of Environmental Protection. Thanks for your time today. We really appreciate it.

Rohit Aggarwala: Thanks for having me, Alison. Appreciate it.

Alison Stewart: That is All Of It for today. Tomorrow, Jane Pratt, she's got a new thing coming. She started Sassy magazine. It's a new Jane Pratt thing. She'll tell us all about it. I'm Alison Stewart. I appreciate you listening and I appreciate you. I will meet you back here next time.