1. United Nations, Department of Economic and Social Affairs, Population Division
https://esa.un.org/unpd/wpp/
2. The State of the World’s Land and Water Resources for Food and Agriculture,2011
3. Water in Crisis: A Guide to the Worlds Fresh Water Resources;Gleick,1993
4. Appraisal and Assessment of World Water Resources
5. Global Map of Irrigation Areas;Siebert,2007