In arid regions groundwater aquifers are one of the main sources of water and they are recharged only through rain. Efficient use of aquifers for drinking or agriculture is extremely important. To utilize this water in an optimum way we need to characterize the aquifer geology, its depth, thickness, and the rate of recharge. We could also increase the recharge rate by redirecting rain waters to these aquifers and use them as natural reservoirs for future use. In this study we characterized the geology of Wadi Qudaid, 80 Km north of Jeddah, Saudi Arabia (KSA) for use as a potential rainwater aquifer. In this work, we collected seismic, electric, and EM data to find the depth to and thickness of the aquifer and compared our results to observations in a nearby well. Seismic data are interpreted using traveltime tomography and early arrival waveform inversion, while EM data are inverted to find the true subsurface resistivity. Seismic tomograms and EM results show the existence of 3 subsurface layers (1) a surface layer consists of sand-silt-gravel, (2) a layer of consolidated sand with some gravel, and (3) a layer of highly fractured igneous rocks.