Life cycle assessments measure water’s impact on Earth’s ecosystems for the first time

Despite water’s significance, modeling how freshwater consumption for drinking, industrial manufacturing, and agriculture has affected ecosystems, human health, and the depletion of nonrenewable freshwater resources has been overlooked. In a new ES&T study (DOI 10.1021/es802423e), researchers take the traditional life-cycle assessment (LCA) approach one huge step beyond current practices with a model that incorporates water consumption.LCA models were created to address problems in industrialized nations, and most of these countries don’t experience human-health risks due to water scarcity, the authors note. Recently, researchers have started to use LCA models to manage diminishing resources in developing countries. To incorporate water consumption into the LCA process, Stephan Pfister, Annette Koehler, and Stefanie Hellweg at the Swiss Federal Institute of Technology Zurich’s (ETH Zurich’s) Institute of Environmental Engineering started from scratch: they created units of measure for water consumption that are compatible with the many values for energy and resource use that appear in an internationally recognized LCA method. “For water use, this hadn’t been done, ever,” says Hellweg, who is a professor of ecological systems design at ETH Zurich.

For example, the team interpreted a well-known value established by the World Health Organization in LCA models and applied it to water use. The disability-adjusted life year is a value that expresses the number of years a person’s life will be shortened as a result of disease or premature death. The team also adapted an indicator applied to address ecosystem impacts and known as PDF (potentially disappeared fraction of species) to express how water impacts species.LCAs routinely rely on aggregated data to represent large areas. But the ecological impacts of water use depend on regional factors, such as freshwater availability, water infrastructure, rainfall, and consumption patterns at a specific location. The team used a geographic information system to gather regional data and divided large rivers, such as the Nile and the Mississippi, into subcatchments. “The watershed level is more appropriate for the assessment, because hydrological processes are connected within watersheds,” Pfister says.

In the paper, Pfister and colleagues demonstrate their model with a case study of a process that is water-intensive worldwide: cotton production. They began with data from the “virtual water” database developed by researchers in The Netherlands. A relatively new idea, virtual water describes the amount of water that evaporates during agricultural use. Specifically, the database is an inventory of the water consumed for agricultural use for many crops in most countries.The team found that the impacts from water consumption in the cotton industry vary according to country: Egypt’s water supply experiences the highest level of damage (77%) from cotton production, whereas Brazil experiences the lowest level of damage (0%), followed by the U.S. (4%).

The damages to ecological systems from overconsumption of water are illustrated in this world map (yellow represents low impacts, navy high impacts).

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