environmentalresearchweb blog

« Wind versus nuclear | Main | Weight matters - on fuel efficiency and vehicle weight »

Water and Transportation Nexus: US Domestic Water for Imported Oil?

Energy and water are inextricably linked. If we consider food as energy, which we should since it is the substance that powers our bodies, then the energy-water nexus is perhaps the most important in the agricultural sector. When we use agriculture to grow crops for biomass that is later converted to liquid fuels, then the energy-water nexus is even more apparent. I calculated how much water is used for driving light duty vehicles (cars, vans, light trucks and sport utility vehicles) and published the results in Environmental Science and Technology (10.1021/es800367m). Results are also summarized in a commentary in Nature Geoscience volume 1.

The results vary from 0.1-0.4 gallons of water per mile (0.2 - 1 L H2O/km) for petroleum gasoline and diesel, non-irrigated corn for E85 vehicles, and non-irrigated soy for biodiesel. Additionally, driving on electricity from the US grid consumes near 0.2-0.3 gallons of water per mile (0.5 - 0.7 L H2O/km). The reason is that water is used to cool off the coal, natural gas, and nuclear power plants on the grid. However, if irrigated corn is used to make E85 ethanol in the United States, then the water consumption jumps by one to two orders of magnitude to 10-110 gallons of water per mile (23-260 L H2O/km), with an average of 28 gallons of water per mile driven. Keep in mind that only about 15-20% of corn bushes are irrigated to any extend in the US.

This information is only an introduction to the energy-water nexus, but the US government is looking at it more closely recently due to research showing how constraints on one side can create problems for the other. This is typified by potential legislation proposed by Senator Bingaman: The Energy and Water Integration Act of 2009. This bill use similar language as in my Env. Sci. and Tech. paper in measuring the life cycle impact of water for transportation in terms of water consumed per distance traveled. Hopefully, research, industry, and government efforts can minimize impacts on water resources and use them wisely for our energy future.

The concept of using water resources sustainably, especially for growing biomass for liquid fuels, makes one wonder about water embodied in imports and exports in general. Is it better for the US to import biofuels from Brazil that are grown from sugar cane that might not stress water resources as much as corn agriculture does in the US? The US has a tariff on imported ethanol, but not imported oil. If the US has an energy policy goal of reducing imports from the Middle East, then it seems like the tariffs would be switched since the US has friendly relations with the Brazilians. So it seems the current US energy policy is to literally trade domestic water for foreign oil. I guess it could be worse.

Posted by Carey King on May 6, 2009 4:03 AM | Permalink