This chapter focuses on determining optimum locations for runoff water harvesting in W. Dahab Watershed, southeastern Sinai, Egypt. A comprehensive approach involving the integration of geographic information systems (GIS), remote sensing (RS), and watershed modeling (WM) was applied through the present work to identify the potential areas for runoff water harvesting (RWH) in Wadi Dahab basin of southern Sinai, Egypt. These tools were effectively used in mapping, investigation, and modeling runoff processes. Eight thematic layers were used as a multi-decision support system (MDSS) for conducting a weighted spatial probability model (WSPM) to determine the potential areas for the RWH. These layers include the volume of the annual flood, basin area, basin length, maximum flow distance, drainage density, basin slope, overland flow distance, and basin infiltration number. The performed WSPM model was run through three different scenarios: (I) equal weights to criteria, (II) weights of criteria are proposed by authors’ experience, and (III) weights are assigned by the sensitivity analysis. The resulted RWH potentiality maps classified the basin into five classes ranging from very low to very high class. According to the audited scenario (scenario 3), the major area of W. Dahab basin is categorized as of high and very high for the RWH potentiality (58.27 and 15.56% of the total watershed area, respectively). The WSPM’s scenario III map gives the results in favor of the other scenarios, whether based on equal weights or those that were assumed by the authors. Four storage dams and five ground cisterns were proposed in the areas of moderate, high, and very high potentialities for the RWH to harvest runoff water and mitigate flash floods hazards.