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Study Finds Water Footprint for Bioenergy Larger Than Other Forms of Energy; Bioelectricity the Smallest, Biodiesel the Largest

Total weighted global average water footprints (blue and green) for major ethanol and biodiesel crops in m3 water per GJ fuel. The yellow marker (also left axis) indicates the total weighted global average WF for bioelectricity from the same crops. The red marker (right axis) indicates liters of water required to produce one liter of fuel. Data: Gerbens-Leenes et al. Click to enlarge.

Researchers at the University of Twente, Netherlands have calculated the water footprints (WFs) of bioenergy from 12 crops that currently contribute the most to global agricultural production: barley, cassava, maize, potato, rapeseed, rice, rye, sorghum, soybean, sugar beet, sugar cane, and wheat. In addition, their study includes jatropha, an energy crop.

In general they found that bioelectricity is more water-efficient than first-generation biofuels (due largely to the ability to use the entire biomass to produce energy, rather than just the starch or oil fraction of the yield for liquid fuel production). They also found that the WF of bioethanol on a m3 of water per GJ of fuel basis appears to be smaller than that of biodiesel. Their results appeared 2 June in an open access paper in the journal Proceedings of the National Academy of Sciences (PNAS).

The WF of a product is defined as the volume of freshwater used for production at the place where it was actually produced. In general, the researchers note, the actual water content of products is negligible compared with their WF, and water use in product life cycles are dominated by the agricultural production stage. The water footprint comprises three components:

  • Green WF: rainwater that evaporated during production, mainly during crop growth.
  • Blue WF: surface and groundwater for irrigation evaporated during crop growth.
  • Gray WF: volume of water that becomes polluted during production.

The study did not include energy inputs in the production chain, such as energy requirements in the agricultural system (e.g., energy use for the production of fertilizers and pesticides) or energy use during the industrial production of the biofuel. As a result, they point out, the study underestimates the WF of bioenergy, most particularly so in cases where agricultural systems have a relatively large energy input.

The WF of bioenergy shows large variation, they found, depending on 3 factors: (i) the crop used, (ii) the climate at the location of production, and (iii) the agricultural practice.

For electricity generation, sugar beet, maize, and sugar cane with WFs of~50m3/GJ are the most favorable crops, followed by barley, rye, and rice with WFs of ~70–80m3/GJ. Rapeseed and jatropha, typical energy crops showing WFs of ~400 m3/GJ, are the least water-efficient. For the production of ethanol, 2 crops grown in a temperate climate (sugar beet and potato) with WFs of ~60 and 100 m3/GJ, respectively, are most efficient, followed by a crop typical for a warm climate, sugar cane, showing a WF just below 110 m3/GJ. Values for maize [corn] and cassava are larger than for sugar beet, sugar cane, and potato at 110 and 125 m3/GJ, respectively. With a WF of ~400m3/GJ, sorghum is by far the most disadvantageous crop. For biodiesel production, soybean and rapeseed, crops mainly grown for food, show the best WF at~400m3/GJ; jatropha has the least favorable WF of ~600 m3/GJ.

—Gerbens-Leenes et al.

Using a different metric, on average it takes 14,000 liters of water to produce one liter of biodiesel from rapeseed or soya. However, the water footprint for rapeseed in Western Europe is significantly smaller than in Asia. For soya, India has a large water footprint, while the figures for countries such as Italy and Paraguay are more favorable. Jatropha, which is increasingly used for biomass production, has an even less favorable water footprint of 20,000 litres of water on average for one litre of biodiesel.

For the production of bioethanol, sugar beet is the best performer with one liter of bioethanol made from sugar beet requiring on average 1,400 litres of water, as against 2,500 liters for sugarcane. Corn requires 2,570 liters of water per liter of ethanol; sorghum requires 9,812 liters of water per liter bioethanol.

The researchers note that the advent of cellulosic biofuels, in which the entire biomass can be used for fuel production, will offer a water footprint more comparable to that of bioelectricity. They assume, though, that the WF of next-generation biofuels will never be lower than the WF of the total crop biomass (m3/ton) divided by the energy content (GJ/ton).

The scientific and the international political communities promote a shift toward renewable energy sources, such as biomass, to limit the emission of greenhouse gases. This study has shown that biomass production goes hand in hand with large water requirements. There are already reasons for profound concern in several regions and countries with limited water resources about whether the food and fiber needs of future generations can be met. If a shift toward a larger contribution from bioenergy to total energy supply takes place, results of this study can be used to select the crops and countries that (under current production circumstances) produce bioenergy in the most water-efficient way.

—Gerbens-Leenes et al.


  • Winnie Gerbens-Leenes, Arjen Y. Hoekstra, and Theo H. van der Meer (2009) The water footprint of bioenergy. PNAS doi: 10.1073/pnas.0812619106



I am little surprised to see Jatropha as the worse case, this is a plant that thrive in semi arid climate, so my guess is that it doesn't require watering or irriguation, also biodiesel require not water in processing the oil of the seed, contrary to ethanol that requires tons of water in the process. Also I don't see palm tree in their comparison. Palm tree producess more biodiesel than any other crop altogether, so why it is not included in their study. Also I wonder how they calculate the amount of water diverted. If you plant a tree you divert a lot of water because the tree need water so store it in its roots, ok but trees do so much to protect and improve the soil, to protect from soil erosion, trees with their deep roots bring nutriement from yards bellow to the surface of the ground, they regulate climate and moisture, they provide storge of CO2 and material for construction. So it is not like this water was wasted.


Sugar beet might requires little water but requires very high quality land and soil and a lot of fertilizer, generates a lot of soil erosion, and last but not least has an EROI close to zero. So it might not require a lot of water but it is a dead end as a source of sugar, they tried in france and gave up, it is not economical


Thats absolutely true


If you have 100 million acres of corn grown in the U.S. each year and you use the grain for food and the stalks and cobs for fuel, I do not see the extra water. With gasification, you can even get the water back out of the biomass for the process.

fred schumacher

Water utilization efficiency becomes critical when a crop is irrigated; however, most of these crops, except for rice, are not normally irrigated. In most locations, they are dryland crops supplied with water by rainfall and snowmelt. Because of the inefficiencies of photosynthesis and the need for plant cooling, most water absorbed by a plant is respired and sent back out into the atmosphere.

Most of the new ethanol plants recycle their processing water, reducing input needs and cost of water treatment. Although the total water quantity may be high, it's not new water all the time, but mostly reused water.

Humans have relied on annual plants to concentrate nutrients for them. Annuals are disturbance plants requiring high inputs and fertility. Perennials are low disturbance, low fertility, low input plants. Certainly for energy production, perennials are the way to go.


I mention corn, because we grow so much for food. Switchgrass is a perennial I guess. I heard that it is replanted every ten years or so. Just mow that once or twice a year and get 1000 gallons of biofuel per acre per year. I don't much care if it is 100 million acres of corn stalks or 10 million acres of switchgrass, I just would like us to get on with making progress and get into massive production ASAP.


I like the idea of using a by-product like corn stalks.


The billion ton study from the DOE showed that you can use about 1/2 the stalks of corn and almost all of the corn cobs for biofuel biomass. The rest is returned to the field for the soil and biochar made from the biofuel process can be put back into the soil as well.


These clowns left out kudzu and switch grass.

It seems all these "researchers" have an ax to grind.


Does anybody research the use of industrial hemp to make bio fuel or is it off limits?


I don't like the idea of using corn stalk,

to leave corn stalk on the ground is absolutely essential to protect the soil from erosion and return nutriement to the soil. If you don't be prepared to the return of dust bowls in the midwest like in the 30s


"Agricultural residues, such as corn stalks, wheat straw, and rice stalks, are normally left on the field, plowed under, or burned.

Collecting just a third of these for biofuel production would allow farmers to reap a sort of second harvest, increasing farm income while leaving enough organic matter to maintain soil health and prevent erosion.

The agricultural residues that could be harvested sustainably in the United States today, for example, could yield 14.5 billion gallons of ethanol—four times the current output—with no additional land demands."


Just 1/3 of stalks and leaves could get us to E10 nationwide with no damage to soils. This does not even count all the corn cobs, that if left in the field, would out gas CO2 and methane, a more potent Greenhouse Gas.


Kudzu is one of the most invasive plants in the world and there is an Early Detection Rapid Response alert in effect for its arrival in Canada.

It's too bad we spent all that money building sewage treatment plants in the Midwest, I wonder if it would not be better to instead ship it to corn fields and fertilize them with natural sewage fertilizer. I wonder what the comparative emissions are of transporting sewage versus making and transporting solid conventional fertilizers.

After all, a good portion of that original fertilizer spread on corn fields makes its way to the sewage treatment plant so it is like recycling!


The Biodiesel that has run my tdi for 85K miles has been made from fryer oil from local resturants. www.azbiodiesel.com is cranking out 20K gallons a week of fryer oil biodiesel and the only water used is to mop the floor and wash a truck from time to time.

Keep cranking out the BS corn lobby, there are still a bunch of fools out there that buy your lies.

fred schumacher

Annuals mine the soil, perennials generate soil. There is a zero sum involved: a plant can concentrate energy, as biomass, either in a seed head or underground root mass, but it can't do both at the same time. Concentrating energy in a seed head is an intensive process. If cellulosic biomass is desired, the worst way to go about it is to grow annual plants to produce it. Using corn stover for cellulosic feedstock is a bad idea, since that biomass is needed to go back into the soil to replace what the plant has taken out. Present state of the art farming methods try to keep as much "trash" as possible in the soil to reduce soil erosion.

Switchgrass, and other C4 photosynthesis pathway grasses like miscanthus, big bluestem, or sugar cane, (commonly called "warm season" grasses), have higher photosynthetic and water utilization efficiency than the common cereal grain C3 annuals like wheat, rice, barley, etc. Corn is a C4 annual, which is why so much of it is grown. It's a more efficient plant. Switchgrass is a long-lived perennial. It would not require replanting on ten year intervals, like sugar cane.

Plant sterility is preferable for a cellulosic biomass feedstock plant. This is one reason Miscanthus giganteus, a naturally occurring sterile hybrid, is such a prolific biomass producer. Since plant phenology is primarily based on growing-degree days, i.e. accumulated heat units, a winter hardy plant like switchgrass can be moved far north of a particular cultivar's point of origin, resulting in virtual sterility, since the more northerly location would not accumulate sufficient heat units to trigger seed set, but would produce more biomass from the longer day length. REAP-Canada has discovered the value of this phenomenon, producing greatest switchgrass biomass yields in Quebec from seed originating in southern Illinois.


I'm with the skeptics here. Why not discuss the water usage of algae? Especially salt water algae? Biofuels must be a part of our energy portfolio to gain Energy Independence. These attempts to discredit energy crops are as hollow as the alarmists decrying CO2!


There seems to be lots of land that we could grow switchgrass on, if there was a market for the biomass. One of the main reasons for the dust bowl was tilling that dried the soil. If you don't till, you don't dry. Leaving the bottom stem and roots of the corn plant in place and no till farming could help.


Mark BC:  If anyone is being paid to watch for kudzu in Canada, you're being ripped off.  Kudzu is not winter-hardy and is no threat to Ohio, let alone Canada.


Kudzu dies back to the ground in winter but resprouts from roots. It has made it to Oregon and New Jersey.


I'm with JosephT. My families biodiesel vehicle runs on fryer oil, which our local fry shops are MORE than happy to part with. I fail to see what additional water footprint this creates.

If given financial incentive, I'm sure McDonald's would provide their fryer oil ensuring every man, woman and child could cross the country a few times over.

If you have strong feelings on water efficiency and/or flooding from global warming, then watch these and send them to people you know. Everyone can help turn climate change around.

black ice

Water is definitely an issue for biofuel production. That is why no one will see biofuel crops grown in Saudi Arabia any time soon. Biofuels can be seen as solar energy bound chemically through photosynthesis, a process that occurs in aqueous media within the cell. Because of this only certain climatic zones are suitable for biofuels. In other places wind, wave, or solar thermal or photovoltaic are options to get the energy which comes from the big natural nuclear fusion reactor - the Sun.


Saudi Arabia is in a precarious situation. They have high population growth but they don't actually have any fresh water except from from the ZamZam well at Mecca. Their 26 million inhabitants rely on desalination from the Persian Gulf and Red Sea. This is energy intensive and requires lots of oil. Furthermore, they are a welfare state dependent on oil revenues, and they can't actually do anything themselves. I wonder what will happen when the oil runs out? I hope by then solar electricity is developed enough so that they can use their deserts to desalinate sea water and irrigate crops.

Also, biofuel production from salt water algae doesn't technically require any water if it's in the ocean.


Treehugger, as a resident of Michigan I have to point out that farmers here have been making sugar from sugar beets for a long time.


Granted, I've no idea how economical it is or what the ROI is, but they're doing it.


Concentrated solar thermal desalinization can generate electricity and create fresh water. You use parabolic troughs like those at Kramer Junction to generate the heat and electric and use the rankine cycle condenser for desalinization. Saudi Arabia and other nations that have lots of sun and are near the ocean can benefit from this.


Once again the Greens easy and ready answers are discovered to have major warts, in practice. Their ill-considered, politicized patent remedies don't work, or have major unexpected problems to them, that are only recognized after $ billions in subsidies.

Windmills, Solar, 1st generation Biofuels, 2nd generation Biofuels, Biodiesel, all turn out to have major drawbacks, and pollution effects of their own, often worse than conventionql energy generation.

Greens exclude the only real renewable that works, Hydro-electric power, that the Greens have somehow decided is not a "genuine Green" renewable. Apparently rain falling amd flowing into rivers and trapped in reservoirs is not a natural, recurring effect, to them.

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