It's not only our carbon footprint we should worry about. Experts are looking for solutions to our growing water foot-print, as urban populations explode and the demand for bio fuels adds stress on water for farmland. The threat to climate change has drawn attention to carbon footprints, the amount of green house gases produced by human activity. Now scientists have begun calculating a water footprint, the amount of water needed to produce goods or services. Are port published this month by UN-ESCO-IHE, the Institute for Water Education in Delft, says it takes 70-400 times as much water to create energy from bio fues as it does from fossil fuels. It said the production of crude oil requires slightly more than one cubic meter of water for one unit of energy, compared with 61 cubic meters to grow biomass in Brazil