Biofuels – their water footprint

We are now growing crops for energy. Some places (such as the European Union) even have targets specifying a given proportion of fuel energy from crops. This practice of growing more and more biofuel has led to food prices of some staples, like maize and rice, becoming very expensive in some places. Using land that presently produces food to produce biofuels is wrong. It is immoral and it is also unsustainable, and one important reason as to why this is unsustainable is the amount of water that these biofuel crops use – known as the water footprint.

The amount of water that crops contain compared with the amount that use is negligible; a water footprint of a crop has three components. The first is the “green water” which is the amount of water evaporated by the plant mainly during growth. The second is the “blue water which is the surface and ground water used for irrigation during growth. The third is “gray water which is the water that becomes polluted during the growth of the plant, or perhaps more accurately the water that is needed to dilute pollutants associated with the crops.

Some Dutch researchers (Winnie Gerbens-Leenesa,1, Arjen Y. Hoekstraa, and Theo H. van der Meerb Department of Water Engineering and Management and Laboratory of Thermal Engineering, University of Twente) have been calculating the water footprint of the more common biofuel and bio energy crops. They have made some interesting findings.

  • Producing bio ethanol uses less water than producing biodiesel
  • Sugar beet, maize and sugar cane are the most favourable crops for producing bio electricity, with a water footprint of 50 cubic metres per gigajoule.
  • Rapeseed and jatropha, typical energy crops, have a massive water footprint of 400 cubic metres per gigjoule.
  • For ethanol production, sugar beet, and potato (60 and 100m3/GJ) are best followed by sugar cane (110 m3/GJ); sorghum (400 m3/GJ) is the worst
  • For biodiesel production, soybean and rapeseed are best averaging 400 m3/GJ; jatropha (beloved of Air New Zealand) has an adverse water footprint of 600m3/GJ.

At the moment 86% of the world fresh water supplies are used for food production and for fibre production. Demand for food is increasing and will increase as the world’s population increases.  The fresh water supply is finite and we must have concerns over whether growing bio fuels particularly for fast cars and small jet aircraft is right, when the same crops could sustain life.

Biofuels are effectively being marketed as a source of renewable energy and as one of the ways of reducing human greenhouse gas emissions. They are marketed as “green, clean and renewable” and therefore as a way to reduce anthropogenic climate change.

They are certainly renewable; with proper land husbandry you can keep growing crops. They are perhaps green in the sense that they comprise vegetation, but in no other sense. They are certainly not clean. Biofuels are made from crops that need vast amounts of precious land and water. With more self control and modest amounts of self denial humans would not need the energy in such quantities.

Large scale growing of biofuels will inevitably affect fresh water supplies. We are not making much new land and we are not making much new water, so biofuel production will take place on land that we need for food crops and water that we need for food crops.

The World Bank has stated that in its opinion the growth of the biofuel industry and the making over of food producing land for biofuel production created the basis for 75% of the food price increase in the past six years.

In my classification of energy fuels ( I classify biofuels as dirty renewables. They are not only dirty but have another effect; they cause us to throw out the baby with the bath water. Literally.


You can read the Dutch study at:

13 Responses

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