While the major media outlets trip over each other reporting on the rising cost of energy, a growing number of resource experts are sounding the alarm that looming water shortages may be an even more significant problem in the next few decades. The severe 2007 drought in the southeastern U.S. was a wake-up call to many who had never thought about water shortages. After all, the region receives an average of 50 inches of rain per year. While in the West, which has traditionally been more focused on drought, long-term water scenarios are downright scary. A recent paper by Scripps Institute scientists says there's a one-in-two chance that the reservoir system of Lake Mead and Lake Powell on the Colorado River, which provides drinking water for 25 million Americans in seven states, will essentially run dry by 2021. The system has already dropped to 50 percent capacity.

Three big problems loom in the West. First, many more people there are dependent on limited water supplies than in the rest of the country. Second, evidence shows that the lower precipitation in the West over the past few decades is a return to the long-term average rather than an aberration; further, allocations from the Colorado River were based on above-average flows. Third, many researchers predict global climate change will significantly alter precipitation patterns, exacerbating drought.

The most important priority for addressing water shortages is to reduce demand by using water more efficiently: flushing toilets with less water, specifying more water-efficient appliances and restaurant equipment, and reducing water loss from cooling towers, for example. In addition to addressing demand, however, we also need to address water supply. There are a number of alternative sources of water that can help satisfy the needs of buildings and the landscapes around them.

The 293-unit Solaire high-rise apartment building in New York City, treats all of its wastewater on-site and uses it for toilet flushing, to supply cooling towers, and for irrigation. Photo courtesy Jeff Goldberg/Esto, Pelli Clarke Pelli

Standard practice in North America is to use the highest-quality potable water for all applications in and around buildings, from drinking fountains to toilet flushing to landscape irrigation. There is rising interest among design teams and building owners in separating potable and nonpotable water flows, however, so that nonpotable sources can be used for applications where the highest purity is not required. Separating water sources and applications in this way opens up a variety of alternative water sources.