SciTech

Research estimates footprint of U.S. economy in water usage

Chris Hendrickson, a professor of civil and environmental engineering who was recently inducted into the National Academy of Engineering, talks about his research on the water usage of all U.S. economic sectors. (credit: J.W. Ramp/Staff) Chris Hendrickson, a professor of civil and environmental engineering who was recently inducted into the National Academy of Engineering, talks about his research on the water usage of all U.S. economic sectors. (credit: J.W. Ramp/Staff)

Did you know manufacturing a dollar’s worth of dog food requires the use of approximately 200 gallons of water? Other industrial processes — such as egg production, electricity generation, and many types of farming — are even more costly in water use per dollar. For example, for one dollar’s worth of output from grain farming, approximately 1,400 gallons of water are used.

These totals, calculated by Carnegie Mellon researchers, consider water use in all steps of a production process. In the case of dog food, there is of course the water used in factory where the dog food is the final product. There also is the water required to raise the meat and nurture the grains used as the raw ingredients. Water is also used in the generation of electricity that powers the factory, and so on.

Carnegie Mellon students Michael Blackhurst and Jordi Sels I Vidal, and professor of civil and environmental engineering Chris Hendrickson, added up the contribution of water use from every economic activity that contributes to the production of dog food, as well as many other industrial processes.

Cobbling together data from disparate sources, such as a water use statistics from the United States Geological Survey and a recent report on water use from the Canadian government, the researchers estimated the total water usage per dollar of economic output for all 427 sectors of the U.S. economy as defined by the Bureau of Economic Analysis.

Before their 2010 paper “Direct and Indirect Water Withdrawals for U.S. Industrial Sectors” was published in Environmental Science & Technology (ES&T), there existed very little data on water use from individual economic sectors. The last comprehensive study of this kind was performed by the U.S. Census Bureau in 1982, so the current work “fills a very important gap,” said University of California at Berkeley professor Arpad Horvath. “They provided a practical piece of research that will be useful for a long time,” he said in a commentary piece also published in ES&T.

Readers should be aware that the study uses national economic data; regional water use data vary widely. However, nationwide figures are useful for informing policy decisions on water.

In future work, Hendrickson and colleagues intend to differentiate different types of water use. For instance, water used for cooling in power generation would be categorized differently from water mixed with other chemicals or used in a chemical reaction.

“We are [currently] trying to make the distinction between renewable water versus non-renewable water that is being taken out of the hydrologic cycle,” Hendrickson said.

Hendrickson is one of the developers of Economic Input-Output Life-Cycle Assessment (EIO-LCA), a method used to estimate the broad impacts of economic activities from greenhouse gas emissions and water use to land use and transportation. Last week he was inducted into the National Academy of Engineering for his contributions in the fields of life-cycle assessment and green design.

The consumption of resources, considered over the life cycle of a single, seemingly simple product, can be enormous, with far-reaching impacts. “Back in the early ’90s, I got interested in green design. We were worried about how to do green computers and green chemical processes. That’s where I started,” Hendrickson explained. Very quickly, he saw that to truly be green in designing products, he needed information on the whole life cycle. “You have got to worry not only about the manufacturing phase, but also the use phase, the disposal phase....”

Twenty years later, Hendrickson is now diagnosing the water-use footprint of the entire U.S. economy.

What shocked Hendrickson the most about his results? It wasn’t that tree nut farming uses more water than melon farming, or that hundreds of gallons of water are consumed in order for Fido or Rover to eat their dinner. Hendrickson takes a more macro view: “My general surprise is just at how much water we use.”