The Faulty Fluid Dynamics of Hotel Environmentalism

i-c515e11e77187da962f223ebd7dc640f-westin_shower.jpgBoskone this past weekend was held at the Westin Waterfront in Boston, which has these funky double showerheads that they charmingly call the “Heavenly(R) Shower” (hype aside, they are very nice showers). The picture at right is courtesy of lannalee on Twitter, as I didn’t bring a camera.

Why am I telling you this? Because there was a sign glued to the wall in the shower that read:

Refresh yourself, restore our world

One of your Heavenly(R) Shower heads has been turned off in an effort to minimize water usage and protect one of our most precious natural resources.

The smarmy enviroweenieness of this was undercut somewhat by the next paragraph, which explained that you could turn it back on by pushing a little button on the showerhead (you can see one side of it on the lower head in the picture). And also by the fact that it’s a completely stupid statement.

Turning off one of the two showerheads does essentially nothing to reduce the water usage. The flow rate of water coming into the shower is determined by the pressure and cross-sectional area of the pipes. If you turn off one of the two showerheads, it just makes the water come out of the other one faster– at twice the speed, in the ideal case, which means you use just as much water per second in the shower with one head as with two. This is why putting your thumb over the end of the garden hose makes the water spray out so much farther– the same amount of water needs to pass through a much smaller opening, so it has to move much faster on the way out. The only way turning one showerhead off can reduce the water usage by making showering slightly less pleasant, and thus getting people to take shorter showers.

But that’s the ideal case– does it hold up in reality? And, more importantly, can we test this?

Of course we can test this– we’re physicists. Well, I am. Also, I’m enough of a dork to want to check this out experimentally.

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