Watch and cringe: Here’s how much ‘invisible’ toilet water sprays into the air after you flush

‘Once you see these videos, you’re never going to think about a toilet flush the same way again.’

BOULDER, Colo. — You may never forget to close the lid again after reading this study — and watching the video below. Scientists have demonstrated how toilet water sprays when we flush — carrying potentially dangerous germs into the air —  in a series of experiments.

Scientists at the University of Colorado at Boulder say the “invisible plume,” which contains microscopic particles of pee, poop and whatever else was in the bowl, is a health hazard for those who follow. The research team used bright green lasers and cameras to reveal for the first time how they are rapidly ejected from a lidless public cubicle.

“If it’s something you can’t see, it’s easy to pretend it doesn’t exist,” says lead author Professor John Crimaldi, a professor of civil, environmental, and architectural engineering, in a statement. “But once you see these videos, you’re never going to think about a toilet flush the same way again. By making dramatic visual images of this process, our study can play an important role in public health messaging.”

Video shows the airborne droplets shoot out at speeds of 6.6 feet per second, reaching 4.9 feet above the toilet within eight seconds. The largest droplets settle onto surfaces. Smaller ones — less than five microns, or one-millionth of a meter — linger suspended for many minutes.

They can transport the gut-turning bacteria E. coli and C. difficile, along with noroviruses and adenoviruses. The virus that causes COVID-19 is present in human waste as well. There is not currently conclusive evidence that it spreads efficiently through toilet aerosols, however.

YouTube video

“People have known toilets emit aerosols, but they haven’t been able to see them,” says Crimaldi. “We show this thing is a much more energetic and rapidly spreading plume than even the people who knew about this understood.”

It’s not only their own waste bathroom patrons have to worry about. The pathogens can persist in the bowl for dozens of flushes, increasing potential exposure risk.

“The goal of the toilet is to effectively remove waste from the bowl, but it’s also doing the opposite, which is spraying a lot of contents upwards,” adds Crimaldi. “Our lab has created a methodology that provides a foundation for improving and mitigating this problem.”

Scientists used two lasers for the study. One shone continuously on and above a toilet, while the other sent out fast pulses of light over the same area. The constant laser revealed where in space the airborne particles were, while the pulsing laser could measure their speed and direction. Meanwhile, two cameras took high resolution images.

The toilet itself was the same kind commonly seen in public bathrooms: a lidless unit accompanied by a cylindrical flushing mechanism.

Frame by frame view of what happens after you flush the toilet.
(Credit: Patrick Campbell / University of Colorado Boulder)

Whether manual or automatic, a flushometer-style valve sticks up from the back near the wall. The brand-new, clean toilet was filled only with tap water.

“We had expected these aerosol particles would just sort of float up, but they came out like a rocket,” notes Crimaldi.

The particles headed mostly upwards and backwards towards the rear wall, but their movement was unpredictable. Similarly, the plume also rose to the lab’s ceiling, and with nowhere else to go, moved outward from the wall and spread forward, into the room. The experimental setup did not include any solid waste or toilet paper in the bowl, and there were no stalls or people moving around.

These real-life variables could all exacerbate the problem, study authors warn.

The team also measured the airborne particles with an optical particle counter, a device that sucks a sample of air in through a small tube and shines a light on it, allowing it to count and measure the particles. Smaller particles not only float in the air for longer, but can escape nose hairs and reach deeper into one’s lungs, making them more dangerous to humans.

A powerful green laser helps visualize the aerosol plumes from a toilet
A powerful green laser helps visualize the aerosol plumes from a toilet while it’s being flushed. (Credit: Patrick Campbell / University of Colorado Boulder)

The disconcerting results shed fresh light on just how many particles end up in the air and what size they are. But they provide experts in plumbing and public health with a consistent way to test improved design, disinfection and ventilation strategies to reduce exposure risk.

“None of those improvements can be done effectively without knowing how the aerosol plume develops and how it’s moving. Being able to see this invisible plume is a game-changer,” says Crimaldi.

The study is published in the journal Scientific Reports.

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South West News Service writer Mark Waghorn contributed to this report.


  1. Yes, I was mocked for telling cloth mask enthusiasts not to wear them into public bathrooms or else they would have this stuff on their face all day. Granted, these are people that think cloth is a bio-suit because their idiot media says so. Thus beyond saving. So we may as well utilize them for cheap asbestos removal.

  2. You said what needed to be said. Sometimes it takes a few more tries to get it to sink in. If they choose to do the opposite, well, Darwin has a saying for that. The main issue is what are we actually going to do about this spray? Can we reduce it with a better lid? Teach people to close, then flush? Who’s going to retro-fit the billions of toilets we have now?

  3. There was an inventor on Shark Tank years ago who had a device to block that spray. They passed… maybe it should be revisited?

    1. That’s exactly what I thought about when I first saw the article. I was trying to look up the invention / episode, but can’t find it.

  4. They were testing a commercial toilet–the kind with no lid that removes the waste with a powerful jet of water. It’s not surprising to see aerosols as shown in the video. I’d like to see a comparison with a typical home unit (the kind with a tank and lid).

  5. This is actually a case of what you don’t know has very likely never hurt you. Truly amazing how society is still flourishing despite the fact that we flush toilets and breathe in the results (and have been doing so since the toilet was invented). We go about our daily lives breathing in the residue from numerous toxins yet continue to live. Life is about your body handling (quite well might I add) things it encounters. You cannot go about living in cloud of fear. Otherwise we all are going to become the proverial “bubble boy”. Could it be that the human immune system handles airborne flush residue with no problem whatsover?? Bottom line… continue to flush your toilets and don’t worry because this is really not an issue.

  6. A surprisingly slanted and worthless article from the normally reliable website. I’m a Doctor of infectious disease; specifically an Infectiologist. Particles that emit into the air after a flush are not harmful in any way. In fact, they are very helpful. Repeated small dose exposure to the toxins found in non-infectious fecal matter will strengthen our immune system. In addition, the average person is exposed to far worse contaminates on a daily basis. Do you think your average teenage fast food worker properly scrubs and rinses all fecal matter from his hands after a bowel movement? And when he later hands you your wrapped hamburger, what do you think is now present on your hands and ultimately in your digestive system? You know the answer. And have you survived all these years? Amazing. Silly article this is. Creating fear where none is warranted.

  7. Toilets have been around for what, over 100 years or more? If this was harmful – we’d know by now. Back to more pressing stories like new cookie recipes or lost dogs.

  8. Now put that green laser on your arse while you fart. You’ll be able to be seen from the space station. Seriously though. This is nothing. Toilets haven’t changed for decades and decades. If this was a problem, there’d be hospitals next to every 7-11. The human body builds up antibodies for all kinds of sh*t – literally! Just take a trip to Mexico or India and eat the local foods and drink the local water. And the latest flu epidemic proves the point. We were forced to be locked up for months and now all those years of antibodies to fight the flu have been flushed down the toilet. Welcome to 2020 war of the worlds.

  9. When I was in my youth I saw high speed video of this as did some of my friends. That would have been some 30-40 years ago. I’ve put the lid down ever since. This is far from the first imagery.

  10. I guess I should stand up and close the lid before flushing. On the other hand, it would be like a light bidet …. slightly refined and refreshing!

    1. This is indeed a good issue! It may not be as frightening as earthquakes, flash floods, tsunamis, wars, plagues and all that, but it’s real and it’s happening all around us affecting our health, everyone, every day …… Kudos to persistent daily life improvement research! Good initial intentions! But what is the solution?
      This problem also bothered me for a while, until I accidentally found a “yoodeer toilet foam dispenser” in the Amazon online store. Oh my God! The game specs have changed! Poseidon’s Kiss has really disappeared! Before you go to the toilet, you press a button and it pumps out a creamy soap foam. The foam quickly covers the toilet water and lasts for a while until you flush it down the pipe. No toilet water splashing your butt, no nasty pee or poop odors, no eyesore dirty bowls, and of course, no ‘invisible’ toilet water sprays! The flushing toilet is there, the soap foam is there, but they’re combined, genius idea! If you’ve ever had a toilet splash or an odor torment, or warry of “invisible plume”,you can try it! This is one of those unique gift ideas you didn’t know you needed until you used it! Please be careful trying it though, I’m worried you’ll never go back ……

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