GWS has prepared many district and regional water development plans thus providing planners and managers with the required information for proper development of the available resources. A separate activity is the advisory role for the construction of low-cost rural water supply schemes in arid and semi-arid areas of East Africa. GWS has expertise to advice on the most appropriate solution available. Often, this involves the study of alternative low-cost options for water supply, such as rain water harvesting by means of roof or rock catchments or small surface water retention structures, such as dams, subsurface dams, sand dams or valley tanks. An other form of rural water development planning is the so-called environmental catchment surveys, in which all relevant aspects of catchments are studied by means of detailed aerial photo interpretation and/or satellite image analysis, and subsequent fieldwork. Land units are classified on the basis of geology, morphology and slope classes while mapping soils, vegetation, erosion, land use and water resources. These baseline data are subsequently translated into water and land resources development and management proposals in which a balanced choice is made for an integrated use of all available natural resources.