Crop Growth Water Use in Ethanol Production

The most water intensive processes in the life cycle of corn-grain ethanol production are growing the feedstock and water used in processing corn to ethanol. Of these, water consumed to grow the crop is the greater of the two. The consumptive use of water is water applied to a crop (by rain or irrigation) that is not returned to a ground or surface water source. For example, in crop production water lost to evapotranspiration is considered consumptive use, while water that percolates to groundwater or returns to stream flow is not consumptive use. To grow a corn crop with rain or irrigation may take the same amount of consumptive water use, but providing that water by irrigation taps aquifer and surface water resources at a greater cost than using rainwater. This cost includes the cost of moving that water to the field, as well as the opportunity cost for other functions that water could perform (for example, industrial or municipal water supply or ecosystem services).

Agriculture accounts for about 85 percent of freshwater consumption in the United States. This includes water used to produce feedstock for biofuel. Groundwater is a primary source of irrigation in the western states in the North Central Region. Rain-fed crop production is primarily in the eastern states of the North Central Region, although all states rely on rain that is available.

Corn grain production uses approximately 22 inches of water, which requires 12 to 20 inches of rainfall or irrigation, during the growing season [1]. Most states in the region rely on rain as the primary water source for corn. It is estimated that 95 percent of all corn-grain ethanol is made from corn grown with rainfall. Nebraska and Kansas lead in the use of irrigation for corn production. There is variation across the region in sources of water used in the ethanol life cycle. The water cost to produce ethanol varies depending on where the corn crop is produced and processed, and whether irrigation is used to produce that crop.

Regional Differences in Water Use for Ethanol

Studies have shown the total field-to-pump water use to produce one gallon of ethanol is between 69 and 207 gallons [2, 3, 4, 5, 6]. However, this data does not take into account the wide variation across the nation in water consumption and the source of the water in crop production. Table 3.3 is a regional comparison of the amount of water embodied in the production of ethanol. “Embodied water” (EWe) is the irrigation water used to produce the corn and the water used in the processing facility. Rainfall is not included. The EWe across the North Central Region ranges from 5 gallons per gallon ethanol in Ohio, to 528 gallons per gallon ethanol in Kansas. This variability represents the differences in rainfall amounts across the region, and the reliance on irrigation for crop production in the more westerly states (figure 3.3).

Figure 3.3 – “Potential biomass resources available in the United States” NREL, 2005.

Table 3.3. EWe and TCW4 in the ethanol producing North Central States in 2007, ranked according to each state’s EWe. Numbers are millions of gallons, unless otherwise specified.

1 EWe = Embedded water in ethanol
2 Wir = Irrigation water
3 Wp = Processing water
4 TCW = Total consumptive water

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