Low-flow faucets have become a standard water-saving feature in public bathrooms. Unfortunately, it turns out that drying your hands can use a lot more water than washing them—anywhere from 18 to 70 liters (4.8 to 18.5 gallons) per hand-washing session, depending on the drying method—according to a life-cycle assessment (LCA) commissioned by Dyson, maker of Airblade high-speed hand dryers. The study, conducted by researchers at the Massachusetts Institute of Technology (MIT), looks at seven hand-drying methods commonly used in public bathrooms.
Photo courtesy Dyson
In general, hand dryers have most of their impact during use—by consuming electricity—while all types of towels have most of their impact during manufacturing. The three high-speed dryers considered in the study won hands-down in every category when pitted against conventional hot-air dryers, paper towels, and reusable cotton roll towels.
Conventional dryers were the worst in terms of global warming potential and water consumption. Both virgin and recycled paper towels tied for a close second in both of those categories. Virgin towels weighed in as the largest energy consumers and the hardest on ecosystem quality. Though their ecosystem effects were smaller, recycled towels are intensive to manufacture and were not far behind virgin towels in energy use.
With any LCA, it’s important to keep assumptions in mind. “Ecosystem quality,” for example, sounds more general than it is: it technically measures “potentially disappeared fraction of plant species per square meter per year” and so would not capture many of the qualities we associate with a thriving ecosystem, like biodiversity or healthy soil.
Many impacts—but particularly water consumption and global warming potential—result directly from energy consumption. For more on why power generation is so water-intensive, see “The Water-Energy Connection.”
Of the common methods, it looks as though high-speed hand dryers are the least energy- and water-intensive way to dry your hands. It would be interesting to see a broader LCA that encompasses both washing and drying; such a study could include alcohol-based hand sanitizer, which consumes neither water nor energy during use and doesn’t require drying at all. And don't forget the lowest-impact solution: drip-drying or using a piece of clothing.
Copyright 2012 by BuildingGreen Inc.