Q: I wonder whether the water pulled out of the air by dehumidifiers is pure and drinkable. How does it compare to distilled water?

Asked by Bill Wachob, '69, from Eggertsville, N.Y.


Of water shortages and gray water

California continues to struggle with the consequences of three years of drought, and its water supply is being pushed to the limit. To learn more about California's water woes, I spoke with Tom Mercer, MBA '09, MS '10, the resident water guru among my fellow Business School grads. In addition to pursuing a joint master's degree in environment and resources, Tom led a student trip last spring with the theme of water production, transportation and consumption in the Western United States. Tom says, "The issue is: there is a finite amount of water, there is a growing number of humans, and humans have inhabited areas where there are scarce water resources." Consequently, some people have come to see more aggressive use of "gray water" as not just part of a solution to water shortages but as a necessity. Gray water is the liquid water output of washing dishes, showering, and brushing your teeth—it's the "used" water in your house that goes down your drain, but not down your toilet.

Gray water can be safe and effective for watering plants, toilet flushing and other applications that don't require potable (safe for drinking) water. The main problem with using more gray water, Mercer says, is that "pretty much every municipality, state and region has different regulations on gray water systems." Mercer is nonetheless optimistic about gray water's future, as many municipalities are looking to relax some of the restrictions on gray water use.

How dehumidifiers work

According to the website HowStuffWorks, dehumidifiers begin by using a fan to draw in ambient indoor air. This air runs over a condensing coil, which, like a glass of cold water, pulls moisture from the air by means of condensation. The drier air is then passed through a warmer coil that returns it to approximately room temperature. The accumulated liquid condensation, called condensate, is collected in a bucket or piped outdoors through a tube. Dehumidifiers come in both built-in and portable models.

Dehumidifiers versus air conditioners

Dehumidifiers only reduce the humidity in the air. Air conditioners cool the air while simultaneously reduce humidity because cool air can't retain as much moisture as warm air. Whether you should use a dehumidifier, air conditioner or both depends on your local ambient air temperature and on the humidity conditions in your home. Visually, you can think of the breakdown with this two-by-two matrix:

  Very humid air Less humid air
Very hot
temperatures
Air conditioner plus
dehumidifier (e.g., Florida)
Air conditioner
(e.g., Arizona)
Cooler
temperatures
Dehumidifier (e.g., Western Massachusetts) Nothing (e.g., San Francisco)


If you live in one of those climates, like Florida's, that has humid air and hot temperatures, you should consider adding an energy-saving dehumidifying heat pipe to your heat pump or central air conditioner. A dehumidifying heat pipe connects to your cooling system and helps it reduce the humidity more effectively as it cools the air.

What to look for when buying a dehumidifier

The first step when buying a dehumidifier is to make sure that it is appropriately sized for your space. That is, it should remove moisture from the air at a rate sufficiently high to make you comfortable but not at so high a rate that you spend more money, or burn more energy, than you need to. Dehumidifiers are sized in terms of the number of pints of water they can remove from the air in 24 hours. Energy Star Northeast website offers a handy calculator to figure out the dehumidifier that's right for you.

The Department of Energy also certifies highly efficient dehumidifier models through its Energy Star program. Since Energy Star models use 10-20 percent less electricity to dehumidify the same amount of space, you can save money on your electric bill and reduce carbon emissions from electricity generation by buying an Energy Star-qualified dehumidifier.

Remember, don't drink the water

In case you didn't see the Essential Answer, dehumidifier condensate (the water that the dehumidifier produces) can be loaded with biological contaminants and metallic residues that are not safe to drink. As this graphic from a Samsung dehumidifier manual advises, please do not drink the water that collects in your dehumidifier.

Potable water-making devices

Going beyond just dehumidification, there are appliances on the market that can make potable water from the air. Two such models suitable for home use are Air2Water's dolphin line, which the company claims can produce clean water at a cost of $0.16 to $0.52 per gallon, and RainCloud's C-15, which costs about $1,000 wholesale. However, these potable water making devices produce water with low to no mineral content, so the water will likely have the same flat taste that distilled water does (see below).

Distilled water: Safe to drink, but not necessarily good to drink

If it weren't for that bad stuff hanging around in your dehumidifier, the condensate wouldn't be terribly different from distilled water. As you may remember from high school chemistry experiments, distilled water is water that has been boiled, evaporated and re-condensed, a process that removes the minerals present in ordinary tap water. Indeed, minerals aren't just found in fancy European bottled waters; it's primarily the collection of local minerals that gives each municipality's water a distinctive taste here in the U.S. Without minerals, water tends to taste flat. Distilled water's lack of minerals makes it suitable for car batteries, for example, where mineral buildup from regular tap water could prevent the battery from working properly. Distilled water is perfectly safe to drink, even if most people find it a little off-putting.

Putting SAGE research ahead of being a good host (and perhaps ahead of common sense as well), I decided to serve distilled water at a dinner party. Perhaps the fact that the bottle said, "may be used in small appliances" instead of "tastes refreshing" should have been my hint to abandon the experiment. Although my guests were good sports about it, they all opted for tap water when it was time for a refill.

Tap water is an important source of vital minerals, such as calcium and magnesium. So, by drinking distilled water, you may be missing out on an easy way to get some of the nutrients your body needs.

Water footprints

Regarding personal actions in the face of water shortages, the aforementioned Mr. Mercer says, "I think it's important to conserve [water] resources in your daily life in ways like not leaving the faucet running, and taking shorter showers." Nevertheless, water use that we can't directly see usually has more of an impact. Mercer says, "It's helpful to think not just about the water you're actually consuming or using . . . but also all of the water that went into producing the things that you eat and that you buy."

Just as each product we buy has a carbon footprint, which corresponds to the amount of carbon dioxide emissions generated in producing and distributing the product, each product also has a corresponding water footprint, which is the water required to produce and distribute the product. It's hard enough to find information about most products' carbon footprints, but it's even rarer to know a product's water footprint. You can start exploring how much of this "virtual" or "embedded" water you're consuming at the Water Footprint Network. While Americans use about 120 gallons of water directly per day on average, we end up using many times that in the products we choose. Wal-Mart's new sustainable product index will require suppliers to provide information about products' water use. Hopefully, other retailers and manufacturers will follow Wal-Mart's lead in this regard, allowing us all to be more conscious water consumers in ways that don't require drinking dehumidifier condensate.


Andy Martin, '02, received his joint MBA/MS from the Graduate School of Business and the Emmett Interdisciplinary Program in Environment and Resources in 2010.