Drying your hands requires far more water than washing them, according to a surprising new manufacturer study.

Low-flow faucets and other water-saving fixtures have become a standard water-saving feature in public bathrooms. Unfortunately, it turns out that drying your hands uses 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. That's according to a life-cycle assessment (LCA) commissioned by Dyson, maker of Airblade high-speed hand dryers.

Hand-drying's worst enemy: hot air

The study, conducted by researchers at the Massachusetts Institute of Technology (MIT), looks at seven hand-drying methods commonly used in public bathrooms and designates Airblade the hand-drying method with the lowest environmental impact in all categories, with the high-speed XLerator dryer coming in second in most of the categories. Strangely, Airblade's higher-performance competitors don't make an appearance (more on this below).

The highest impact in most impact categories, based on the research parameters, comes from standard warm-air hand dryers.

Paper or power?

All electric hand dryers have the vast majority of their impact during use--primarily through energy consumption. Hence, those that consume less energy have a lower impact; the Airblade wins out over the XLerator, according to the study, because it takes less time to completely dry hands and has an electronic motor that does not waste energy on "spin-down." Presumably, any high-speed hand dryer sharing these characteristics would have similarly low impacts. Both Airblade and XLerator won hands-down over paper towels--both virgin and recycled. All the towel drying methods have the vast majority of their impact during manufacturing, which explains why recycled paper towels, which are manufactured in much the same way as virgin towels, have similar energy, global warming potential (GWP), and water use impacts but do better in terms of ecosystem health.

Towels' greater impact is due mainly to their disposability: even reusable cotton roll towels have a short life, so many thousands of towels would be manufactured and shipped during the five-year life of a typical hand dryer.

Looking at the whole life cycle

The LCA considers each method's entire life cycle, from resource acquisition to disposal, including everything from the water used to generate electricity for manufacturing and use--hence the high water consumption for all methods--to the global warming potential (GWP) of plastic trashcan liners used for throwing out paper towels. In a thorough "sensitivity analysis," it even takes into account a number of what-ifs--looking at how different the results would be if paper towels were composted instead of landfilled and what would happen if you used each cotton roll towel 130 times instead of 103.

These extra steps help mitigate concerns about biased assumptions, and the study results do generally make sense. BuildingGreen did a far less formal LCA of various hand-drying methods way back in 2002, when the then-pioneering XLerator came on the market, and came to much the same conclusion about paper towels vs. high-speed hand dryers.

Study covers emissions--also suffers from omissions

While the Airblade comes out looking clean (and dry) as a whistle in the study, it's important to keep in mind that LCA is an imperfect tool for assessing environmental impacts. These book-length reports look thorough and include more data--and more details about how the data came to be--than you can shake a stick at, but there can be significant omissions.

In this case, the most glaring one is that the hand dryer brands most similar to the Airblade, such as the Mitsubishi Jet Towel, were not included in the study results. We look forward to seeing equally thorough comparative LCAs from others in the industry--including manufacturers of high-speed hand dryers whose energy performance may equal or exceed that of the Airblade.

Checking the paper trail

In addition, paper towel manufacturers have argued with Dyson's LCA conclusions before. Kimberly-Clark, for example, has faulted Dyson for not taking hygiene into consideration in its research; the company distributes a brochure titled "Are 'High Speed' Dryers Really Worth the Risk?" (PDF) in which it claims that the Airblade increases bacteria on hands 42% while disposable paper towels reduce bacteria on hands 77%.

While Dyson has publicly questioned such claims, its latest LCA does not take hygiene into consideration at all--an odd oversight, given that hygiene is the primary justification for hand-washing in the first place. If your drying method makes them less clean, the environmental impacts hardly seem worth it.

Drying our hands with water and carbon

While we wait for more data that perhaps takes hygiene into account in addition to dryness, it's worth considering that even the Airblade dryer uses 18 liters of water and contributes 4 g of CO2 to the atmosphere every single time you use it. Isn't drip-drying or wiping hands on clothing an option? We'd also love to see an LCA of alcohol-based hand sanitizer added to the mix.

Meanwhile, watch for the January issue of Environmental Building News for a deep look at product transparency and how to get what you need from such reports while also taking them with a grain of salt.