With water becoming a scarce commodity, intensive use of water for bio­energy cannot be considered sustainable if water extraction is affecting ag­riculture, domestic use or causing environmental impacts. Being an aquat­ic species, algae require more water than terrestrial bio-energy plants and when cultivated in open ponds there are great water losses mainly through evaporation. According to Williams and Laurens [93] the dissociation of one mol of water occurs for every mol of CO2 required in the photosyn­thetic process. In their study of water use in algal cultivation Murphy and Allen [94] calculate that 33.2 m3/m2 of water per year is required to culti­vate algae in a raceway pond in the United States. It is possible to recycle much of the water that is drained from the ponds during harvesting but there will be losses in harvesting the algae; freshwater must therefore be sourced. In the same study it was reported that the management of the water will require seven times the amount of energy that can be produced from biodiesel extracted from the algae [94]. The majority of countries around the world are becoming increasingly water stressed and therefore using extra freshwater in biofuel production is not sustainable. The use of wastewater as an alternative to freshwater provides an ideal solution how­ever freshwater would still be necessary for downstream processing of the biomass or for dilution of highly concentrated wastewater.