Splash-free Urinals Inspired by Nautilus Shells and Dogs

The practice of marking territory with urine is repulsive to most people; ironically, about half of the world's population (males) inadvertently marks bathroom floors, and themselves, through unintentional urinal splash back. This problem has persisted since the invention of the urinal over a century ago. We found that when a liquid jet or droplet train impacts a rigid surface below a certain critical impinging angle, almost no splatter is generated. Thus, a surface designed to always intersect the urine stream equal to or smaller than the critical angle prevents splash back. Inspired by nautilus shells and dog urination, we designed urinal surface geometries that effectively eliminate splatter by satisfying the splash-suppressing intersect criteria. Our numerical and experimental validations show that our urinal designs are superior to the typical use of a popular urinal available on the market as well as scenarios where urine steams are highly unstable (e.g. urinals in ships and airplanes undergo perturbation). Our new urinal designs will keep bathrooms cleaner and reduce the labor, water, and chemicals required for periodic cleaning to promote more sustainable bathroom maintenance.