Biofuels, such as ethanol and biodiesel, are an alternative to petroleum- based transportation fuels and are produced in the United States from a variety of renewable sources such as corn, sugar cane, and soybeans. Ethanol, the most common U.S. biofuel, is mainly used as a gasoline additive in blends of about 10 percent ethanol and 90 percent gasoline, known as E10, which is available in most states. A relatively small volume is also blended at a higher level called E85—a blend of 85 percent ethanol and 15 percent gasoline—which can only be used in specially designed vehicles, known as flexible fuel vehicles. Biodiesel is a renewable alternative fuel produced from a range of plant oils, animal fats, and recycled cooking oils. Pure biodiesel or biodiesel blended with petroleum diesel—generally in a blend of 20 percent biodiesel and 80 percent diesel—can be used to fuel diesel vehicles. The federal government has promoted biofuels as an alternative to petroleum-based fuels since the 1970s, and production of ethanol from corn starch reached 9 billion gallons in 2008. The Energy Policy Act of 2005 originally created an RFS that generally required U.S. transportation fuel to contain 4 billion gallons of renewable fuels in 2006 and 7.5 billion gallons in 2012. EISA expanded the RFS by requiring that U.S. transportation fuel contain 9 billion gallons of renewable fuels in 2008 and increasing this amount annually to 36 billion gallons in 2022. Moreover, the 36-billion-gallon total must include at least 21 billion gallons of advanced biofuels, defined as renewable fuels other than ethanol derived from corn starch that meet certain criteria; only 15 billion of the 36 billion gallons of renewable fuels can come from conventional biofuels. In addition, at least 16 billion gallons of the 21-billion-gallon advanced biofuels requirement must be made from cellulosic feedstocks, such as perennial grasses, crop residue, and woody biomass. Unlike corn starch, most of the energy in plant and tree biomass is locked away in complex cellulose and hemicellulose molecules, and technologies to produce biofuels economically from this type of feedstock are still being developed. Some cellulosic biorefineries are piloting the use of biochemical processes, in which microbes and enzymes break down these complex plant molecules to produce ethanol, while others are piloting the use of thermochemical processes, which use heat and chemical catalysts to convert plant material into a liquid that more closely resembles petroleum. There are a number of steps in the biofuels life cycle, from cultivation of the feedstock through distribution to the end user at the fuel pump (see fig. 1). Water plays a critical role in many aspects of this life cycle. On the cultivation side, water is needed to grow the feedstock. Crops can be either rainfed, with all water requirements provided by natural precipitation and soil moisture, or irrigated, with at least some portion of water requirements met through applied water from surface or groundwater sources. Figure 2 shows the various water inputs (sources of water) and outputs (water losses) that are part of the agricultural water cycle. Water is also important for conversion of feedstocks into biofuels. In particular, water is used for heating and cooling as well as for processing. For example, during the processing of corn-based ethanol, corn is converted to ethanol through fermentation using one of two standard processes, dry milling or wet milling. The main difference is the initial treatment of the corn kernel. In the dry-mill process, the kernel is first ground into flour meal and processed without separating the components of the corn kernel. The meal is then slurried with water to form a mash, and enzymes are added to convert the starch in the mash to a fermentable sugar. The sugar is then fermented and distilled to produce ethanol. In the wet-mill process, the corn kernel is steeped in a mixture of water and sulfurous acid that helps separate the kernel into starch, germ, and fiber components. The starch that remains after this separation can then be fermented and distilled into fuel ethanol. Traditional dry-mill ethanol plants cost less to construct and operate than wet-mill plants, but yield fewer marketable co-products. Dry-mill plants produce distiller’s grains (that can be used as cattle feed) and carbon dioxide (that can be used to carbonate soft drinks) as co-products, while wet-mill plants produce many more co-products, including corn oil, carbon dioxide, corn gluten meal, and corn gluten feed. The majority of ethanol biorefineries in the United States are dry-mill facilities. Figure 3 depicts the conversion process for a typical dry-mill biorefinery. The extent to which increased biofuel production will affect the nation’s water resources will depend on which feedstocks are selected for production and which areas of the country they are produced in. Specifically, increases in corn cultivation in areas that are highly dependent on irrigated water could have greater impacts on water availability than if the corn is cultivated in areas that primarily produce rainfed crops. In addition, most experts believe that greater corn production, regardless of where it is produced, may cause greater impairments to water quality than other feedstocks, because corn production generally relies on greater chemical inputs and the related chemical runoff will impact water bodies. In contrast, many experts expect next generation feedstocks to require less water and provide some water quality benefits, but even with these feedstocks the effects on water resources will largely depend on which feedstock is selected, and where and how these feedstocks are grown. Similarly, the conversion of feedstocks into biofuels may also affect water supply and water quality, but these effects also vary by feedstock chosen and type of biofuel produced. Many experts agree that as the agriculture and biofuel production industries make decisions about which feedstocks to grow and where to locate or expand conversion facilities, it will be important for them to consider regional differences and potential impacts on water resources. Many experts and officials told us that corn cultivation requires substantial quantities of water, although the amount used depends on where the crop is grown and how much irrigation water is used. The primary corn production regions are in the upper and lower Midwest and include 12 states classified as USDA farm production Regions 5, 6, and 7. Together, these regions accounted for 89 percent of corn production in 2007 and 2008, and 95 percent of ethanol production in the United States in 2007. Corn cultivation in these three regions averages anywhere from 7 to 321 gallons of irrigation water for every gallon of ethanol produced, as shown in table 1. However, the impact of corn cultivation on water supplies in these regions varies considerably. For example, in USDA Region 7, which comprises North Dakota, South Dakota, Kansas, and Nebraska, the production of one bushel of corn consumes an average of 865 gallons of freshwater from irrigation. In contrast, in USDA Regions 5 and 6, which comprise Iowa, Illinois, Indiana, Ohio, Missouri, Minnesota, Wisconsin, and Michigan, corn is mostly rainfed and only requires on average 19 to 38 gallons of supplemental irrigation water per bushel. The effects of increased corn production for ethanol on water supplies are likely to be greatest in water-constrained regions of the United States where corn is grown using irrigation. For example, some of the largest increases in corn acres (1.1 million acres) are projected to occur in the Northern Plains region, which is already a water constrained region. Parts of this region draw heavily from the Ogallala Aquifer, where water withdrawals are already greater than the natural recharge rate from precipitation. A 2009 USGS report found water levels in the aquifer had dropped more than 150 feet in parts of southwest Kansas and the Texas Panhandle, where crop irrigation is intense and recharge to the aquifer is minimal. In 2000, about 97 percent of the water withdrawn from the aquifer was used for irrigation, according to USGS. Many officials told us that an increase in corn cultivation using current agricultural practices will also impair water quality as a result of the runoff of fertilizer into lakes and streams. This will happen because corn requires high applications of fertilizers relative to soybeans and other potential biofuel feedstocks, such as perennial grasses. For example, in Iowa, the expansion of biofuel production has already led to an increasing amount of land dedicated to corn and other row crops, resulting in surface water impacts, including nutrient runoff and increased bacteria counts as well as leaching of nitrogen and phosphorus into groundwater, according to a state official. Fertilizer runoff containing nitrogen and phosphorus can lead to overenrichment and excessive growth of algae in surface waters. In some waters, such enrichment has resulted in harmful algal blooms, decreased water clarity, and reduced oxygen in the water, which impair aquatic life. In marine waters, this excessive algal growth has created “dead zones,” which cannot support fish or any other organism that needs oxygen to survive. The number of reported dead zones around the world has increased since the 1960s to more than 400. Many of them are along the Gulf of Mexico and the Atlantic Coast, areas that receive drainage from agricultural and urban landscapes, including a large portion of the Corn Belt, where many of the existing and planned ethanol production facilities are located. A 2007 USGS model estimated that 52 percent of the nitrogen and 25 percent of the phosphorus entering the Gulf system are from corn and soybean cultivation in the Mississippi River basin. Increased corn production will also increase the use of pesticides— including insecticides and herbicides—which also have the potential to affect surface water and groundwater quality. For example, a 10-year nationwide study by USGS detected pesticides in 97 percent of streams in agricultural and urban watersheds. As would be expected, the highest concentrations of pesticides have been found in those areas that have the highest use.