Runoff-farming, a water harvesting technique, is the diversion of rain water from a collecting area to a cropping area, thereby increasing the quantity of water available for crop growth. This technique, applicable in various types, is regarded as necessary to secure and increase food production in semi-arid regions. Simultaneously it minimizes water erosion risk where it is applied. As the potential of runoff-farming has not been investigated, a methodology had to be developed to enable planners to identify suitable areas the most efficient way. Five main information sources are tapped: ground checks by various specialists, maps, data, aerial photographs and satellite images. The interpretation of the collected data yields in the quantification of the runoff water, the water requirements of the crops and the water storage capacity of the soil. All factors have to be validated and integrated into a decision model.