A general assumption among the American public—and even some sectors of the green community—is that saving water and saving energy go hand in hand. In some cases, that can be true. A dishwasher that uses less water, for example, typically uses less energy because there is less water to heat.

However, it is a myth to think that this is always true. In fact, water is often forgotten in the energy equation and vice versa, a misstep that could have huge implications on our future water and energy supplies.

In his book Unquenchable, author Robert Glennon says that one of the biggest examples of this is ethanol. Although many people think ethanol is the perfect solution for our country’s reliance on oil, it takes more than 4 gallons of water to refine each gallon of ethanol.

And that, Glennon says, doesn’t even take into account the fact that farmers must first grow the corn to make that ethanol. According to Glennon, in the American West, where many new ethanol plants are located, it may take as much as 2,500 gallons of irrigated water to produce enough corn for 1 gallon of ethanol. To put it in perspective: The state of California has a goal of producing 1 billion gallons of ethanol per year. However, accomplishing that would take more water than now goes through the Bay Delta to supply Southern California cities and Central Valley farmers. (In case you were wondering, that’s a whopping 1.7 trillion gallons of water.)

And ethanol isn’t the only example. In his paper, "Solar Energy’s Cloudy Future," Glennon analyzes the large amounts of water used by concentrating solar power (CSP) systems. Although a growing alternative energy solution in some states like Arizona, Glennon states that CSP plants use a substantial amount of water in their cooling systems.

These types of energy/water misconceptions can trickle down to some technologies you may be considering for your builds. As Mary Ann Dickinson, president and CEO of the Alliance for Water Efficiency, said in an earlier Vision 2020 interview, green roofs installed in dry areas like Arizona need to use alternative sources of irrigation in order to be truly efficient. If the roof is using imported water that has to be pumped and treated—as opposed to greywater or rain water—it is probably using more energy than if a traditional roof was installed.

As Glennon points out, just as the energy industry uses lots of water, the water industry uses lots of energy. The U.S. has an estimated 60,000 water systems and 15,000 wastewater systems that consume 3% of the nation’s energy to take water on a very inefficient journey of pumping, transporting, treating, distributing, collecting, and then treating again. According to a 2005 California Energy Commission report, water-related energy use consumes 19% of the state’s electricity, as well as 30% of its natural gas and 88 billion gallons of diesel fuel every year.

The fact is that energy and water need to be considered together—not as separate entities—as we march toward sustainability. Glennon clearly puts it in perspective: “The reality is that we don’t have enough energy or water.”