Airports are hell, but Singapore’s Changi Airport is—for the jet set—a little slice of travel heaven. The world’s best airport for the fourth consecutive year boasts a rooftop pool, 24-hour cinema, butterfly garden, and spas—all surrounded by lush vegetation to make you forget you’re stuck in a concrete and steel jungle waiting to board an aluminum tube.

So if you’re Changi Airport and you want to top yourself, you have to go big. Bold. Ostentatious. You bring in WET, the water design firm that designs fountains for famously over-the-top places like the Bellagio, Burj Khalifa, and the Sochi Olympics. When the airport’s newest structure designed by architect Moshe Safdie opens in 2018, it will boast the Rain Vortex, the world’s tallest indoor waterfall.

Construction on new glass building that will house Rain Vortex began this summer. “It’s a huge toroid of glass,” says WET founder Mark Fuller. Or, to put it in less mathematical terms, it’s like a huge glass bagel, complete with the hole in the middle. It is through this hole that water will fall nine stories, dropping into what looks like a second waterfall that begins at ground level. To spice it up even more, WET is also choreographing light shows that make the waterfall glow. No one has ever built anything like it.

Changi Airport and Safdie Architects

And because no one has ever cut a giant hole in a bagel-shaped glass roof and dropped water nine stories to the ground, the engineers on the project were concerned. “A natural waterfall, it actually creates it own microclimate,” says Fuller. Think about it: A waterfall is water crashing through the air and dragging that air with it. It creates turbulence. It makes clouds of mist. The last thing you want is a terminal full of hot, humid air. You expect that in LaGuardia, not the world’s best airport.

After a bunch of airflow studies of the glass dome, the WET team’s solution was to change up the flow of the waterfall. The effects of the turbulence build up over time. By alternating lighter trickles with sheet-like cascades, the waterfall doesn’t actually disrupt the air in the building all that much.

To perfect the flow, the team began by mocking up a one-fifth scale model of the waterfall. Water can be tricky to scale because it does not flow a fifth as fast in a one-fifth scale model. “You’re not scaling gravity. You’re not scaling viscosity,” says Tony Freitas, the lead WET engineer on the project, ticking off the forces that affect water flow. So it actually takes extra math to convert the results from a scale model to what you would expect in the real thing. WET also built a full-sized prototype of one-third of the waterfall’s edge, just to make sure water would behave as they expected. And because even that was too big to test in doors, they hoisted it up by crane at the Hansen Dam in LA, where they poured gallons and gallons over the edge of the partial model.

Scale model of the Rain Vortex. WET

The basic forces at work on the waterfall’s edge are the ones that hydraulic engineers consider when building weirs, structures that alter flow of a river. Weirs, in fact, look like squat, mini waterfalls. “The hydraulics are very simple,” says Arturo Leon, a hydraulic engineer at the University of Houston, “but the architecture is very, very impressive.” The conceptual leap from weirs to a nine-story circular waterfall is what makes the whole project interesting.

The Rain Vortex takes inspiration, as you might expect from the name, from rainfall. It storms a lot in Singapore, and the Rain Vortex will run on rainwater collected on the building’s bagel-shaped roof. During heavy storms, it might be dumping as much as 10,000 gallons of water a minute. This ability to reuse rain is key because Singapore, despite all its rainfall, has to import a lot of water from Malaysia, a long-simmering source of tension between the two countries. Freitas says rainwater should be enough to keep the Rain Vortex running, but they can pump in more water if needed.

It’s hard not to notice that WET often designs huge water features in water-challenged places: Las Vegas, Dubai, and now Singapore. Fuller has his own way of looking at it. “When you take the amount that’s evaporated away in the Bellagio Fountain,” he says, “and you divide by the number of people that watch it, it’s less than a toilet flush. Do you get more joy doing that or flushing your john?” You’ll have plenty of time to ponder the next time your flight is delayed.