Water footprint of bio-energy and other primary energy carriers

Freshwater is essential for life on earth, not only for basic human needs such as food, fibre and drinking water, but also for a healthy environment. In the near future, important challenges are to meet basic needs and to ensure that the extraction of water does not affect freshwater ecosystems. At present, humanity already uses 26 percent of the total terrestrial evapotranspiration and 54 percent of accessible runoff. If the world population increases further, there is concern in several regions and countries with limited water resources if food and fibre needs of future generations can be met. In general, global change is often considered in relation to climate change caused by emissions of greenhouse gasses, such as CO2 from fossil energy carriers. A shift towards CO2-neutral energy carriers, such as biomass, is heavily promoted. Nowadays, the production of biomass for food and fibre in agriculture requires about 86% of the worldwide freshwater use often competing with other uses such as urban supply and industrial activities. A shift from fossil energy towards energy from biomass puts additional pressure on freshwater resources. This report assesses the water footprint (WF) of bio-energy and other primary energy carriers. It focuses on primary energy carriers and expresses the WF as the amount of water consumed to produce a unit of energy (m3/GJ). The report observes large differences among the WF’s for specific types of primary energy carriers. For the fossil energy carriers, the WF increases in the following order: uranium (0.09 m3/GJ), natural gas (0.11 m3/GJ), coal (0.16 m3/GJ), and finally crude oil (1.06 m3/GJ). Renewable energy carriers show large differences in their WF. The WF for wind energy is negligible, for solar thermal energy 0.30 m3/GJ, but for hydropower 22.3 m3/GJ. For biomass, the WF depends on crop type, agricultural production system and climate. The WF of average biomass grown in the Netherlands is 24 m3/GJ, in the US 58 m3/GJ, in Brazil 61 m3/GJ, and in Zimbabwe 143 m3/GJ. Based on the average per capita energy use in western societies (100 GJ/capita/year), a mix from coal, crude oil, natural gas and uranium requires about 35 m3/capita/year. If the same amount of energy is generated through the growth of biomass in a high productive agricultural system, as applied in the Netherlands, the WF is 2420 m3. The WF of biomass is 70 to 400 times larger than the WF of the other primary energy carriers (excluding hydropower). The trend towards larger energy use in combination with increasing contribution of energy from biomass to supply will bring with it a need for more water. This causes competition with other claims, such as water for food crops