Jeroen Willems

A Happier World · 28 September 2026

Sewers Can Warn Us About The Next Big Virus

After more than two years, I have finally published a new A Happier World video!

This time I explored the connection between a hidden river in Brussels, a visit by Bill Gates to the city’s sewers, and pandemic prevention.

I interviewed Jeff Kaufman and Will Bradshaw from SecureBio Detection (formerly the Nucleic Acid Observatory), people working at Sciensano (essentially the CDC of Belgium), and someone from the Brussels Sewer Museum.

Script

1. Introduction

Why would one of the richest men on earth visit a smelly sewer?12

Why did the river in Brussels disappear?

And what do both of these things have to do with preventing the next pandemic?

News clips / interview montage:

French poet Charles Baudelaire famously called the river a big open-air toilet.

Check your toilet and just like what you’ll find there…

Well, it does stink.

No one wants to talk about it or go anywhere near it.

There’s a lot more to wastewater than meets the eye.

It seems like such a wealth of information is in our waste.

So what makes the Brussels sewer system so interesting that Bill Gates would rather visit smelly, rat-infested tunnels than enjoy our amazing waffles, fries, beer or chocolate? Well, it wasn’t for some weird billionaire hobby. One reason is the dark history behind the sewer. Let’s rewind a bit…

2. History of the Senne

What would you do if covid happened in the 19th century?

Imagine a world without masks, vaccines, or modern medicine. A world where doctors didn’t even wash their hands yet… What would you do if a highly contagious disease, something like COVID-19, swept through your city?

This terrifying scenario is exactly what Brussels, like many other cities at the time, faced in the 19th century.

Jeroen on location: I am currently in the Brussels Sewer Museum. Attentive viewers might recognize this location from a previous video of mine. There is a difference this time around. You can’t actually see the water flowing because there’s construction going on, but they let me show a part of it, so it’s all good.

What I didn’t mention last time is that this actually isn’t the sewer system, but the Senne: a river that used to flow through Brussels but that they covered up because it was spreading diseases.

Do not mix up the Senne with the Seine, its famous Parisian cousin. Sure, the Seine gets all the postcards, but the Senne carved her own niche in Brussels’ history.3

The people of Brussels, also called Brusseleirs, directly disposed of their waste into the Senne. As a result, the river became an open-air sewer, prone to overflowing during even the lightest rainfall. And if you’ve ever been to Belgium, you know it rains a lot here.

Sophie Vanderschueren: Er bestond nog geen zuivering van ons afvalwater. Dus alle ambachtelijke activiteiten, ons organisch afval, kwam uiteindelijk terecht in de Zenne. Dat zorgde voor heel veel stank en ook het brengen van ziektes zoals cholera epidemieën.

There was no purification of our wastewater yet. So all artisanal activities, our organic waste, eventually ended up in the Senne. This caused a lot of stench and also disease outbreaks such as cholera epidemics.

Most people at the time thought it was the awful smell that caused the epidemics ravaging Brussels. While not entirely accurate, they were on to something. Human waste caused much of the stink in the air and it also happened to carry heavy doses of the cholera microbe.

And it’s this human waste that contaminated the groundwater that the Brusseleirs drank. No wonder diseases spread so easily!45

Frustrated with floods and disease, the Brusseleirs had enough. Plans were hatched to cover the Senne. Construction from 1867 to 1871 buried the river. Modern boulevards were built on top of the hidden waterway. This wasn’t without controversy. Many homes, businesses and breweries got displaced during the process, and the move was championed by the infamous King Leopold II. Remember the guy, with the rubber obsession and the really bad reputation for exploiting Congo? Yeah, that guy.678

Outside of the city, the river still flows out in the open, but in the city it’s all covered. I’m currently standing next to the last remaining visible part of the original Senne in the city center. The actual river has moved to help with flooding, so this isn’t even a river anymore. And while the Senne might be hidden, the connection between our sewer system and our health certainly hasn’t disappeared.

Sophie Vanderschueren: Het heeft nu een functie van stormbekken, maar de Zenne stroomt daar niet meer. De Zenne stroomt nu hier, waar de oranje kleur is. En wij zijn hier ongeveer, dus de Zenne stroomt wel degelijk onder onze voeten.

It now functions as a storm basin, but the Senne no longer flows there. The Senne flows here now, where the orange color is. And we’re approximately here, so the Senne does flow under our feet.

3. The Problem: Detecting Pandemics

Why detecting pandemics with wastewater makes more sense than alternatives

Today we would rather not hear anything anymore about covid or pandemics. But unfortunately, despite our modern medicine, the risk of a new pandemic has never been higher, and just having experienced one doesn’t change that. Never before did we fly so many planes, spreading diseases wherever we go. Never before did we farm so many animals so close together, creating a perfect breeding ground for new pandemics. And never before was it this easy to engineer deadlier viruses.

The sobering truth is that the next pandemic could be just around the corner, and it could be even more devastating.91011

So what can we do? Can we stop it before it even starts?

Viruses replicate and spread to more and more people. This means that even a few cases can quickly turn into a big outbreak.12

So responding just a few weeks earlier can mean the difference between containment and a global catastrophe.13

Testing individuals is slow and expensive. During the pandemic, health officials struggled to keep up with new cases and many at-home tests never reached them.14 Since we can’t test every single person on the planet, all the time, there’s got to be a better way.

There may be a glimmer of hope in the unlikeliest of places.

News clips:

Valuable tool in pandemic response.

Wastewater.

Wastewater testing.

Surveillance of wastewater can serve as an early warning system that could one day help prepare us for the next pandemic.

Turns out, traces of viruses like COVID-19 or polio show up in our poop, even before we have symptoms. So since everyone uses the toilet, wastewater gives us a great snapshot of what’s circulating in a community.

It may sound gross, but our sewers are full of valuable information.

Will Bradshaw: So wastewater has seen a huge explosion of interest since the COVID pandemic. A lot of countries are now monitoring wastewater actively when they weren’t before. And relative to other forms of monitoring, wastewater has a lot of good properties. It’s comparatively cheap, it’s easy, it’s non-invasive, it preserves privacy, and it allows you to detect infections across a whole population, including people who don’t otherwise have symptoms.

This means wastewater signals can provide days or even weeks of advance notice compared to conventional testing, acting like an early warning system.

And since wastewater is anonymous, it can’t tell that you are sick, only that someone is, we don’t need to work with people’s personal medical information.15

It’s also a proven tool in the fight against polio, flu and respiratory virus outbreaks. Studies have used wastewater to track community stress levels, food-borne illnesses, obesity trends, drug use patterns and even the spread of antibiotic-resistant infections. This information is invaluable for improving health policies and saving lives.1617181920

What Sciensano does

Here in Belgium, scientists at Sciensano are at the forefront of wastewater monitoring, covering nearly half of the Belgian population.21 The public health institute played a crucial role in tracking the COVID-19 pandemic over the past few years.

Koenraad Van Hoorde: So we started with SARS-CoV-2, from this year on, we will also start the surveillance of influenza and RSV. And we also started with polio.

Bavo Verhaegen: So once a week we receive wastewater samples from all over Belgium. So we get the samples as raw material like this. So it’s just an aliquot of a sampling taken over 24 hours.

Bavo Verhaegen: So to analyze the samples, we employ a PCR. What’s a PCR? We look for specific regions in the RNA that is specific for Sars-Cov-2.

Bavo Verhaegen: We look for this region and we will start to multiply it so much that it starts to become visible.22

Current detection systems only look for known pandemics & future pandemics might be a lot worse

So right now, wastewater monitoring can tell us the levels of known viruses like COVID-19 or polio. But what if a brand new virus emerges, something we’ve never seen before?

This is important because nature isn’t the only source of new pathogens. Biotechnology is becoming increasingly more advanced and more affordable each year, with DNA sequencing costs decreasing rapidly. This has amazing benefits for curing diseases. And as you’ll see later, it can help us fight pandemics too. But there is also a major downside.

Historically, organized groups and state-sponsored programs have tried to weaponize biological agents. With advancements in biotechnology, such efforts could pose a greater threat in the future.

Jeff Kaufman: One way that the world is changing a lot right now is that AI is moving very quickly and we’re sort of moving into a period of time where people who don’t have much biological knowledge may be able to use AI systems to sort of fill in their various knowledge gaps and it could become much easier for individuals who want to cause harm by creating a pandemic to do that without needing to go to grad school and become a virologist. This means that the work that we’re doing is becoming increasingly urgent because the kinds of things that we would hope to never find are becoming increasingly likely.

However, the risks extend beyond malicious intent. One group of researchers has successfully modified strains of bird flu in ferrets so it can spread through the air.23 The benefits of such research are questionable, and the risks are too great. Lab leaks happen, even in the most secure labs. Since 2000, at least 50 pathogens have leaked, infecting over 300 people and killing 8.2425 And there’s still ongoing debate as to whether the COVID-19 pandemic was the result of a lab leak or not.

So, if we face a future where a lab leak or a bioweapon could unleash a virus that’s as deadly as the plague, which killed half of Europe in the Middle Ages, then we need to be prepared to detect and respond to emerging threats.26

Koenraad Van Hoorde: So current methods still lack sufficient sensitivity to really look for something unknown. We still rely on multiplying the target we are looking for. But I think in the future the technology will allow us really to look for everything and also the things that we are not yet familiar with or that we do not know yet.

So what can we do?

If we only rely on spotting pathogens we already know, we’ll be playing catch-up whenever something new appears. So we need better technologies, and that’s where projects like the Nucleic Acid Observatory come in.

Jeff Kaufman: I’m Jeff Kaufman. I co-lead the Nucleic Acid Observatory, which is a project of the research nonprofit SecureBio that aims to detect novel pathogens, new viruses or bacteria that might be spreading through the population. We look for new methods to detect any biological threats through wastewater or other environmental samples.2728

Jeff Kaufman: There are two main kinds of wastewater monitoring, the kind that you see almost everywhere, where if you see a graph of like, here’s what COVID is doing in this sewer shed, that is based on PCR-based monitoring. This is a system that lets you look for a specific known thing matching a genetic sequence. This is really useful if you want to track known things. But we are trying to track unknown things.

Will Bradshaw: If you’re trying to do unknown monitoring for unknown things, you’re more likely to do what’s called untargeted metagenomic sequencing. Which is you sequence everything that’s in there, and you get a big pile of sequences, and then you sort through those sequences to find ones that are potentially concerning.

Will Bradshaw: There are several options that we’re exploring, but none of them are really mature yet. One is that you can look for things that are growing. You can say, well, we don’t know what this pathogen will look like exactly, but we know that in order to be threatening, it has to grow and be abundant throughout the population. Another option might be that you look for new things. But you can imagine if you sequence at the same treatment plant for a year, characterize everything that’s in there, and then look for stuff that’s new that’s showing up for the first time. A slightly more esoteric way is if you’re worried about deliberate threats, you can look for things that are genetically engineered.

Will Bradshaw: Cost is definitely a big issue with the techniques that we’re looking at. Sequencing, DNA sequencing is expensive and the more sequencing you do, the more expensive it is. And as I said, because new pathogens are rare, you might need to do a lot of it. That said, sequencing has gotten cheaper very quickly over the past decade and I expect it to continue getting cheaper. I expect within five years, for example, sequencing to be orders of magnitude cheaper than it is now.

Will Bradshaw: You don’t necessarily need to be doing this monitoring for unknown things everywhere in the world that you’re doing wastewater monitoring. It’s possible that, for example, concentrating your efforts in terms of novel detection in a few places, for example, the world’s largest airports or the world’s largest cities, could be a much more cost-effective approach.

Will Bradshaw: Partly because, for most cities, if a new pathogen comes into that city, it’s going to do it through the airport. But also because treatment plant waste, in addition to human sewage, also contains industrial runoff, rainwater, restaurant waste, maybe agricultural waste. Airplane waste is much more pure human sample.

Jeff Kaufman: Another advantage of getting samples from airplanes is by sampling in one place, you can get information about the sort of broader world because you have international flights coming from all over and depositing at this one location.

Jeff Kaufman: Over the past year, we’ve done quite a lot of different things. I think the main one is that we’re now running a pilot biosurveillance system where we are actually collecting samples from a bunch of different sewer sheds and we are sequencing them. In addition to collecting and sequencing samples, we also have a genetic engineering detection system that we’re now running on all the incoming data.

Jeff Kaufman: We are only monitoring the US. Even within the US, we’re only monitoring a handful of cities. It would be great to have much more widespread monitoring, both within the US and globally.

So detecting new threats isn’t going to be cheap or easy straight away, but the potential benefits are priceless. It’s a great example of how science and technology can help us create A Happier World. If you would like to learn about more great ideas like this, consider subscribing and hit the bell to get notified when new videos come out.

The Brussels sewers & Senne today

Today, a sprawling 200-mile network of sewers and treatment plants clean the city’s waste. And while the Senne might be hidden in the city center, it’s still linked to Brussels’ wastewater.

Sophie Vanderschueren: Dus dat zijn gewoon kleinere riooltjes die uitmonden in grote rioolcollectoren zoals deze.

So those are just smaller sewers that drain into large sewer collectors like this one.

Sophie Vanderschueren: En die rioolcollectoren gaan dan uiteindelijk naar de rioolwaterzuiveringsstations.

And those sewer collectors then eventually go to the wastewater treatment plants.

Sophie Vanderschueren: Tenzij het regent, dan kan het ook overstorten naar de Zenne of het kanaal.

Unless it rains, then it can also overflow into the Senne or the canal.

Sophie Vanderschueren: Dit is dus eigenlijk een overstort. Dat is een soort venster die de link maakt tussen de riolen en de Zenne die daarachter stroomt.

So this is actually a kind of window that makes the link between the sewers and the Senne that flows behind it.

I witnessed this myself when I visited the museum again to film some extra footage.

This happens approximately 7 times a month. Yikes.29303132

When there’s so much rain even the Senne can’t handle it, the sewage ends up in the Brussels canal. Because there are no barriers or filtration, everything, including rats, ends up in the water, continuing the Senne’s legacy of an open-air sewer.33

But Brussels isn’t alone. In Paris too, the wastewater overflows into the Seine whenever it rains too much. Cities like London and Copenhagen are also battling sewage overflow and flood risks with massive billion-dollar infrastructure projects.3435

4. Takeaways

Circle back to Bill Gates

Speaking of billions, why did one of the world’s richest men visit a stinky sewer? Well, it turns out that Bill Gates is passionate about preventing the next pandemic. He was already raising awareness of the issue before 2020. Because he understands the power of wastewater monitoring, he decided to visit the Sewer Museum on World Toilet Day to highlight the solution.

Koenraad Van Hoorde: Well, it’s not something that happens every day to meet someone like Bill Gates. And then the fact that I had the opportunity to tell him a little bit more on our wastewater surveillance activities and how it is used here in Belgium for public health, it was a great honor.

Sophie Vanderschueren: En dus ja, daar is Bill Gates naar buiten gegaan. Dat is normaal gezien niet voor de bezoekers, maar rioolwerkers van Vivaqua komen wel langs daar naar binnen.

And so yeah, that’s where Bill Gates exited the sewer. Normally, that’s not for visitors, but Vivaqua sewer workers do come in there.

Bill Gates (TED Talk): If anything kills over 10 million people in the next few decades, it’s most likely to be a highly infectious virus.

Whatever you may think of Bill Gates, he brings our attention to an important idea. We can prevent future pandemics, which could be worse than COVID-19, by testing our wastewater for unknown pathogens. This is less invasive than testing individuals, so we need to do more research and take action now. The question is, can we do it in time?

Jeff Kaufman: I think we continue to need to work to get costs down. We need to improve our detection methods. But beyond that, we also need to talk to people in governments around the world and show them what is possible. I think this is very promising, and this is something that many more public health agencies around the world should be looking into.

Will Bradshaw: There are now many countries, I think most developed countries are now doing some form of wastewater monitoring, and it’s also been quite popular in developing countries as well. That said, we have seen a degree of decline in wastewater monitoring since the end of the COVID pandemic, with some countries scaling back their investments in this area.

Will Bradshaw: I think it’s really important that we don’t make the mistake of dismantling the systems that we have in place to detect a new thing. We have an opportunity now for the first time to build a monitoring system that can detect future things and will keep us safe. And I think we should take that opportunity.

Outro

Wastewater monitoring offers a glimmer of hope, a way to detect threats before they spiral out of control.

So the next time you flush a toilet, remember, sewers aren’t just smelly tunnels for our excrement; they can be a frontline in pandemic detection and prevention. So let’s appreciate the science flowing beneath our cities.

Bill Gates (TED Talk): If we start now, we can be ready for the next epidemic.

And guess what? Brussels is bringing the Senne river back. Well, a portion of it at least. The “Max-sur-Senne” project is going to uncover 650 meters of the old river here.36 The construction is set to start in early 2025.37

Jeroen 2026 clip 2, same location:

So… That never happened. I guess I’m not the only one who’s late! The project got shelved for budgetary reasons.383940 But at least the global story is still encouraging!

Sciensano started screening for flu, RSV, and polio as planned.4142

The Nucleic Acid Observatory is now called SecureBio Detection and they expanded their wastewater monitoring to over 31 sites across 19 US cities!

And it’s already paying off: they’ve detected measles in their network more than 20 times, including a single case in a city of over a million people.4344 Their genetic engineering detection pipeline has also flagged a harmless engineered virus from vaccine research.45

However, risks from engineered pandemics are increasing as AI models get more capable464748495051, so scaling up this technology is becoming more important than ever.52

Does your city or town have a hidden river or waterway like Brussels? Or maybe even underground tunnels, an abandoned treatment plant or sewer-dwelling legends? Let’s hear those interesting local facts. Share your stories in the comments.

Other sources

These are sources I used that don’t back one specific line: background reading, footage and images.

Background reading

Footage and images

Stock footage, images and dashboards, in order of appearance

Canal It Up (now City to Ocean)

Maps of Brussels and the Senne

Old photos and paintings

Footnotes

  1. https://www.instagram.com/reel/Cz1FCF_sfQn/?hl=en ↩

  2. https://www.brusselstimes.com/804922/it-stinks-bill-gates-visits-brussels-sewer-system-tbtb ↩

  3. https://www.brusselslife.be/en/article/under-brussels-the-senne ↩

  4. https://www.brusselslife.be/en/article/under-brussels-the-senne ↩

  5. https://baludik.fr/parcours/3523-the-senne-runs-through-our-veins/ ↩

  6. https://www.brusselslife.be/en/article/under-brussels-the-senne ↩

  7. https://baludik.fr/parcours/3523-the-senne-runs-through-our-veins/ ↩

  8. https://patrimoine.brussels/liens/publications-numeriques/versions-pdf/bvah/les-boulevards-du-centre ↩

  9. https://ourworldindata.org/coronavirus ↩

  10. https://www.worldbank.org/en/publication/wdr2022/brief/chapter-1-introduction-the-economic-impacts-of-the-covid-19-crisis ↩

  11. https://www.sciencedirect.com/science/article/pii/S0264999323003632 ↩

  12. https://forum.effectivealtruism.org/posts/gLPEAFicFBW8BKCnr/announcing-the-nucleic-acid-observatory-project-for-early ↩

  13. https://forum.effectivealtruism.org/posts/gLPEAFicFBW8BKCnr/announcing-the-nucleic-acid-observatory-project-for-early ↩

  14. https://www.latimes.com/california/story/2022-03-21/sewage-surveillance-covid-infectious-diseases-future ↩

  15. https://naobservatory.org/reports/comparing-sampling-strategies-for-early-detection-of-stealth-biothreats/ ↩

  16. https://www.latimes.com/california/story/2022-03-21/sewage-surveillance-covid-infectious-diseases-future ↩

  17. https://sitn.hms.harvard.edu/flash/2023/something-in-the-sewage-what-watching-our-wastewater-can-tell-us-about-infectious-diseases/ ↩

  18. https://www.youtube.com/watch?v=NpXL_khUXQQ ↩

  19. https://healthpolicy.fsi.stanford.edu/news/benefits-wastewater-surveillance-combating-infectious-diseases ↩

  20. Bill Gates, How to Prevent the Next Pandemic (2022), chapter 3 ↩

  21. https://www.sciensano.be/nl/projecten/nationale-surveillance-van-sars-cov-2-en-zijn-varianten-afvalwater (archived) ↩

  22. https://en.wikipedia.org/wiki/DNA_sequencing ↩

  23. http://www.wired.com/2012/06/fouchier-h5n1 ↩

  24. https://www.thelancet.com/journals/lanmic/article/PIIS2666-5247(23)00319-1/fulltext ↩

  25. https://www.chathamhouse.org/laboratory-accidents-and-biocontainment-breaches/background ↩

  26. https://www.historytoday.com/archive/black-death-greatest-catastrophe-ever ↩

  27. https://forum.effectivealtruism.org/posts/gLPEAFicFBW8BKCnr/announcing-the-nucleic-acid-observatory-project-for-early ↩

  28. https://naobservatory.org ↩

  29. https://weatherandclimate.com/compare-london-and-brussels ↩

  30. https://www.vrt.be/vrtnws/nl/2024/02/08/canal-it-up-plaatst-borden-voor-brusselse-weggebruikers-die-onwe/ ↩

  31. https://www.citytoocean.org/en/senne-panels/ ↩

  32. https://www.citytoocean.org/en/home-en/ ↩

  33. https://www.citytoocean.org/en/sainctelette-sewage-overflow/ ↩

  34. https://www.citytoocean.org/en/sainctelette-sewage-overflow/ ↩

  35. https://www.youtube.com/watch?v=S26CHpcD2zk ↩

  36. https://www.brusselstimes.com/145600/brussels-will-uncover-part-of-buried-senne-river-environment-maximilian-park-biodiversity-mobility-alain-maron ↩

  37. https://www.maxsurzenne.brussels/le-projet?lang=nl (archived) ↩

  38. https://www.bruxellestoday.be/actualite/parc-maximilien-renove.html ↩

  39. https://www.bruzz.be/actua/stedenbouw/plannen-voor-openlegging-zenne-maximiliaanpark-hold-geen-budget-2025-07-16 ↩

  40. https://www.bruzz.be/actua/stedenbouw/stad-zet-door-met-nieuwe-kinderboerderij-en-vernieuwd-maximiliaanpark-2025-09-09 ↩

  41. https://wastewater.sciensano.be/dashboard/respiratoryviruses/en/ ↩

  42. https://hdl.handle.net/20.500.14493/12843 ↩

  43. https://securebio.org/blog/updates-nov-2025/ ↩

  44. https://securebio.org/blog/updates-mar-2026/ ↩

  45. https://securebio.org/casper/ ↩

  46. https://www.anthropic.com/threat-intelligence-report-september-2026#biological-misuse-sep-26 ↩

  47. https://www.cnn.com/2026/09/10/health/anthropic-bioweapons-report ↩

  48. https://www.nytimes.com/2026/08/06/science/ai-viruses-bacteria-arc.html ↩

  49. https://www.technologyreview.com/2026/09/18/1144329/the-specter-of-ai-enabled-bioweapons-is-a-wake-up-call-for-biotech/ ↩

  50. https://www.semafor.com/article/09/03/2026/experts-warn-of-threats-of-ai-bioterrorism ↩

  51. https://thebulletin.org/2026/09/newly-created-viruses-are-a-warning-we-still-have-a-window-to-stop-ai-enabled-bioweapons/ ↩

  52. https://www.rand.org/pubs/research_reports/RRA4999-1.html ↩