Physicists Make a Splash With a Urinal That Doesn't

At the American Physical Society's Division of Fluid Dynamics meeting in Indianapolis in fall 2022, the team made a splash with a design for a urinal that, well, doesn't. The splashless urinal's shape is inspired by the geometry of a nautilus shell, and prevents droplets from leaving the bowl.

The team identified the need for a better urinal in exactly the way you'd expect. "We are physicists. We use urinals. We all got splashback on our tan pants sometimes and [on our] bare feet in summer, and were embarrassed," says Dr. Zhao Pan, assistant professor of mechanical and mechatronics engineering at the University of Waterloo, via email. He is the head of the lab that created the idea for the new urinal, dubbed the "Nauti-loo."

Droplets don't stay in a typical urinal, explained research assistant Kaveeshan Akan Thurairajah, because "current designs are not optimized to prevent splash, and often have this as an afterthought. You can study science, engineering and mathematics, and head to the bathroom after class and get droplets on your pants. If we can get a man on the moon, a rover on Mars and split the atom, then surely, we can pee without splashing."

While it may seem simple, there is in fact quite a bit of physics involved in urinal design. The slope and angle of the porcelain, plus the height of the person using it and the force of the stream all dictate whether splashing happens. When the University of Waterloo team used dyed water and a mock ureter to simulate the use of a standard urinal, they saw significant splashing. Those drops would have ended up all over people's legs and feet and the bathroom floor.

"Most of us do realize that droplets are being spread, but probably don't realize how bad it is," says Thurairajah. "This is partly due to the fact that sticky floors are the result of multiple trips, and also the biases in our head; clearly the mess is others' and not myself."

In reality, unless it's been recently and thoroughly cleaned, the average bathroom is absolutely covered in droplets.

To solve the problem, the scientists focused on one splash factor, says Thurairajah, called "impinging angle." In other words, the angle at which the stream and the porcelain meet. They found that, below 30 degrees, there was no splash. "Thus, we called this a critical angle," he says. "We wanted a curve which always intersects the trajectory at this angle. This is the same curve as a nautilus shell."

The nautilus is a kind of mollusk — a relative of the squid and octopus — that moves by expelling water from its shell. The shell's spiral shape is considered mathematically "perfect"; it's a visual representation of the Fibonacci sequence, which was introduced in the Middle Ages as part of the foundation of natural geometry.

The nautilus shell has been an emblem of math and science since the days of the ancient Greeks, who considered its symmetrical shell a symbol of perfection. It's the name Jules Verne gave to Captain Nemo's submarine in his novel "Twenty Thousand Leagues Under the Sea," and the title of a popular science magazine.

Now, it may also become known as the inspiration for, and namesake of, a better place to pee.

"The next steps are securing intellectual property protection and then manufacturing," says Thurairajah. "We do hope to see this in bathrooms." Switching to the Nauti-loo, the scientists hope, will make bathrooms a more sanitary place, and help "save water, chemicals and the effort required to clean."