This One System Inventory (OSI) Water Atlas is prepared for the Main Nile sub-basin. The Atlas is essentially provided with maps, charts and general information/brief descriptions about the sub-basins land, climate, hydrology, infrastructure and utilities, and few environmental issues. The sub-basin maps included are location, administrative, population density, elevation, shaded relief, terrain/landscape classification, surficial geology, dominant soils, rainfall, temperature, evaporation, humidity, sub-catchment drainage network, runoff, vegetation cover, landuse/landcover, isoerodent/sediment yield and malaria-prone areas. Whereas schematics of indicative water balance are presented for the main rivers of the EN sub-basins, maps showing existing and potential irrigation and hydropower projects are not incorporated.