A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

Urinal 101: Aim for the back wall or the water?

May 9, 2003

Dear Cecil:

I conducted due diligence at your Web site, but found no reference to a delicate but vital question that has been nagging me for some time now. Can you please tell me whether it is more sanitary to aim directly for the back wall of a urinal or to splash into the water? Which minimizes splashback? Do urinal designers consider this in the same way that, say, auto designers use wind tunnels to minimize air resistance? This question takes on heightened urgency when I visit guests' homes and the issue of auditory embarrassment is considered.

Cecil replies:

Certain parties, and they're not all necessarily female parties, are now rolling their eyes and making eww-ick noises, the wusses. I'm sorry, but there are things the world needs to know. We'll call this discussion Men Are Pigs, Part Two.

Men Are Pigs, Part One, which surely few have forgotten, dealt with the question of why toilet seats in public restrooms are U-shaped. Answer: To eliminate the part that men are most likely to scuzz up. Urinal design is intended to address a similar problem. Some men, of whom your fastidious columnist is one, can use a urinal without soaking themselves and the floor in the process. However, if we judge from the swamplike condition of the average men's room, the percentage of men who have mastered this useful art is not large. The principal difficulty, which will surprise few women, is improper aim.

For a view from the trenches, as it were, I spoke to Gary Uhl, director of design for American Standard, one of the leading makers of toilet fixtures. Gary told me that considerable thought has gone into the design of the modern urinal in order to eliminate splashback. The rear wall of the typical urinal is parabolic in cross section when viewed from above, and the porcelain finish is conducive to laminar flow. The principles of fluid dynamics tell us that a fluid striking a smooth surface at an oblique angle will tend to flow along that surface. Assuming the source of the fluid is near the focal point of the parabola — and modesty makes it unlikely he'll stray too far — the fluid will run straight down the urinal wall with little or no splashing.

I asked Gary if there were a "sweet spot" at which users should aim to minimize splashback. He said no. Clearly, however, certain assumptions are being made, the foremost of which is that the user is going to aim for the back wall. (Actually, assumption number one is that the user is going to aim, period.) But some men, such as you, Mathias, wonder whether they should "splash into the water." You'd think the answer would be obvious. Since it isn't, let me put the matter plainly: If you splash into the water, you knucklehead, the water is going to splash on you.

But men don't listen. What then to do? Several approaches have been advanced:

(1) Build a splashproof urinal. See for example www.marketlaunchers.com/wilkins.html. Part of the idea with this design is to make the urinal deeper and more concave. I'm sure it's an improvement. The only problem is that it looks like a huge white . . . well, let's just say you feel like you ought to cover it with a giant fig leaf. You're not getting me to use this thing in public.

(2) Try to make the best of a bad situation. A number of vendors offer urinal drain screens with ribbed designs said to reduce splashback. These mitigate the negative consequences when the lads aim for the deodorant cakes. But to my mind, such screens are a halfway measure at best.

(3) Give men something higher to shoot for. Now we're talking. Gary tells me that management at the international terminal of New York's Kennedy airport specified that the image of a black fly be printed on the porcelain at the center of the back wall of every urinal. When given a target, it seems, men instinctively aim at it. The fly was originally introduced at the Schiphol airport in Amsterdam, where it supposedly reduced spillage by 80 percent. Side benefit: Folks who've seen these urinals never again utter the cliche, "I wish I were a fly on the wall."

One final note: It has nothing to do with urinals, but you did mention "auditory embarrassment." (What, you want me to believe you're visiting people who've got urinals in their homes?) If you ever have occasion to build or renovate a bathroom, and the plumber asks you if you want the soil stack (the main drainpipe for the toilets) made out of plastic instead of the traditional cast iron, say no. Cast iron muffles sound; plastic, also known as polyvinyl chloride or PVC, amplifies it. Oh, ga-ross, you say. But someday you may be glad to know.

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