Pee Splash Science

So here's the deal, if you stand when you use the toilet, pee splashes back on you, on your shoes, and on your clothes. And if you share a bathroom with someone who stands when they pee, a fine layer of pee covers your entire bathroom.

How do we know this? Well, we aren't psychic, and we haven't been prowling around in your bathroom, but we are scientists - and few people understand the science behind peeing like we do.

When liquids fall through the air, they break into smaller droplets, as the surface tension of the liquid pulls them apart. The technical term for this is Plateau-Rayleigh instability. So, the further the urine stream has to travel through the air, the more likely the stream is to be pulled apart into hundreds of tiny droplets. Imagine standing and peeing from the top of the Empire State building, and what that urine stream would look like when it hits the sidewalk below. Even on the calmest of days, it would not resemble a stream in any way, but would land more like a light rain shower on the pedestrians below. (If the thought of that made you smile, your sense of humor is just as bad as ours.)
                                                                                                                                                                            The image below was taken with a high-speed camera, showing a needle dispensing water from a height of approximately 1 inch. As you can see, even this small amount of liquid can quickly turn from a solid stream into a number of independent droplets as it falls through the air this short distance. You can only imagine what happens when the typical volume of urine travels the average distance of 24 inches into a toilet. 
These droplets of urine splash more than a stream of urine would, and this is why the floor of most public bathrooms are sticky. Good luck getting that thought out of your head for the next 30 seconds. But don’t worry, we fixed it. 

How you ask? Well, we know this sounds counter intuitive, but to minimize splashing, the user has to move in closer to the toilet. We designed the UrineAide® to bring the user in as close as possible to the toilet, but without the need for looking down, stooping over, or even aiming. The result – no pee splash.

Along with getting closer to the target, you also have to adjust the entry angle to reduce pee splash. When liquids strike any surface (like porcelain for instance), at an angle between 50 and 90 degrees, the impact velocity immediately turns the stream into droplets that splash in every direction. 

This image shows the dispersion of the splash, when an opject strikes a surface at a non-ideal angle.                                                                                                       
This as a major hurdle, since the angle at which most users pee is more or less fixed, as a force of habit. So we created a nozzle for the UrineAide® that was adjustable in 360 degrees, allowing the user to set the perfect entry angle into the toilet.                                                                                                                             
The entry angle issue is compounded by the velocity of the falling liquid. The faster the liquid is moving as it hits the water inside the toilet, the more pee splash back occurs. To fix this we introduced a precise series of bends to the downspout of the UrineAide® which serve to constrict the flow of liquid, without ever allowing the UrineAide® to fill up or overflow.                                                 
Now lets talk about speed. Actually not speed - but velocity. The faster a liquid is moving when it hits a surface, the more energetic is the effect of the splash that it makes. Basically, increased velocity only adds fuel to the fire when we're talking about pee splash.                                                                                        
To remedy this, we put on our engineering hats, pulled out our calculators and got to work. A little fluid dynamics math, combined with a significant amount of experimentation taught us a lot. To decrease the velocity of the liquid as it moves through the UrineAide®, we introduced a series of precise bends at exact angles allowing the liquid to flow at a consistent speed regardless of the amount of pressure being exerted.
When we first started working on the UrineAide® we never would have guessed that so much science could fit into a package so small. The concepts that power the UrineAide® are simple, but combining all of these concepts into a single device has proven to a be rewarding challenge. We love what we have created, and we know that you will too. Photos Courtesy Of: Brigham Young University Splash Lab