Friday, August 20, 2010

Foto Phriday - Phunny Math

I've already talked about the green waterless No-Flush(TM) urinals at our office building. Here's a photo of a portion of the instruction sign posted near the thing. Notice the claim that it saves about 45,000 gallons of water per year.

Let's do some math, shall we?

(45,000 gallons/year) x (1 year/365 days) x (1 day/24 hours) x (4 quarts/gallon) x (1 flush/quart (est.)) = ~20.5 flushes/hour

So, assuming that my estimate of 1 quart of water per flush is pretty accurate, then the replaced loos would have had to have been flushed every three minutes, all day, every day of the week in order to achieve the claimed savings. Of course, the "approximately" in the claim could be translated to "within three orders of magnitude," but that would be silly.

This building has a fairly traditional 8-hour workday, but the start times are staggered. Let's assume that the bathrooms are in steady use from 7:00am through 5:00pm. So then, if we need to compress the flushes from 24 hours to 10 hours, that means that we'd need to flush about 49 times per hour. Not likely.

Marketing strikes again.

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