Hey Mr. Green,

During a drought, is it better to clean the house with paper towels or with cloth rags that need to be washed? We have a Kenmore front-loading washer, which the Internet says uses 17.28 gallons per load. —Heather, in Redwood City, California

Because of the extreme variability in the personal use of rags and paper towels, and the many kinds of paper towels available, this question is impossible to answer definitely. But undaunted by impossibility, I forge on in search of ever-elusive truths.

Your washer has a capacity of 3.1 cubic feet. So I first selected a rag that was about 3 feet square (18 by 26 inches), loosely balled it up, and calculated its volume by the time-honored formula of V = 4/3 πr³. Allowing for space around each rumpled rag of this size, I figured that you could fit about 24 in a 3-cubic-foot washer. I then filled up my own 3-cubic-foot washer with a collection of these rags, and to my immense delight, I found that it could hold about the same number as indicated by my computation—not exactly as big a deal as finding the Higgs boson or calculating the gravitational force of dark matter at the birth of the universe, but gratifying nonetheless. So, dividing the 17.28 gallons by 72 square feet, I concluded that your machine would use about a quarter of a gallon of water per square foot of rag.

I then obtained a roll of paper towels that contained 53.2 square feet, put it on a kitchen scale, and found that it weighed a half pound. I consulted the American Forestry and Paper Association’s Sustainability Report which states that it takes 5 gallons to make a pound of paper, so my half pound of paper towels would’ve required 2.5 gallons, meaning that each square foot would’ve required about .05 gallons, or only one-fifth the amount of water as washing the rags.

But since it probably takes about five times as much footage of paper towels as rags to cope with the equivalent messes, the two are probably tied as far as water consumption is concerned. Which is to say, it looks like an, um, wash.

Far more important in the grand scheme of things is the fact that you have a relatively efficient modern washing machine. Washers that were made before 1998 use twice as much water as newer brands that meet federal standards, and three times as much water as today’s Energy Star models, which take 15 gallons or less per cycle, or 8 gallons less than non–Energy Star models. An Energy Star washer will use 27,000 fewer gallons over its lifetime than other machines and also consume far less gas and electricity.

Finally, if you do use paper towels, opt for recycled ones, because every ton of recycled paper saves an estimated 7,000 gallons of water, according to a report from Green Seal, an organization that certifies the sustainability of various products. —Bob Schildgen

Got a question? Ask Mr. Green!

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 --illustration by Little Friends of Printmaking