7 Green and Blue Water Aditya Sood, Prathapar Sanmugam, and Vladimir Smakhtin 7.1 Introduction Researchers are always looking for new approaches to tackle obstinate problems. While in some cases these approaches represent fundamentally new methods of addressing an issue, in other cases they simply constitute a changed perception for the same one. If the change in perception leads to a complete change in societal view of an issue, it is a paradigm shift (Kuhn, 1962). One such shift relates to water management for agricultural production, which is critical to development and will remain so as human population increases and diets shift toward more water demanding food. A sustained effort in improving water and crop productivity in recent decades—exemplified by the Green Revolution of the1960s and 70s—has allowed food production to outpace human demand (FAO, 1996). However, the point has been reached when low hanging fruits, associated with raising productivity in irrigated areas, have largely been exhausted. As a result, recent discourse is moving toward improving productivity in rainfed agri- culture, especially in the African continent where agriculture is predomi- nantly rainfed and productivity is low. To aid in this effort, colors have been utilized to highlight the difference between water management for rainfed versus irrigated agriculture. Traditionally, in water resource management, colors have been used to define water streams in the realm of domestic wastewater management (Otterpohl et al., 1999; Otterpohl, 2002; Gaulke, 2006; Bester et al., 2008; Daigger, 2009). Four colors are predominantly used to define domestic wastewater. Yellow water is the urine component and the brown water is the water mixed with human feces (Linder, 2007), i.e., toilet wastewater minus yellow water. Black water is a technical term used to define toilet wastewater, i.e., combination of yellow and brown water. Finally, grey water is all of the remaining domestic wastewater, i.e., domestic wastewater without black water. More recently, the two colors increasingly used in discourse in agricultural water management are green and blue. The role of green water in agriculture has received growing recognition for its ability to foster food security and 1111 2 3 4 5 6 7 8 9 1011 1 2 3111 4 5 6 7 8 9 20111 1 2 3 4 5 6 7 8 9 30111 1 2 3 4 35 6 7 8 9 40111 1 2 3 4 45111 6162 KEY CONCEPTS WATER RESOURCE-A2_234x156 mm 04/03/2014 13:08 Page 91 1ST PROOFS NOT FOR DISTRIBUTION