Ground-based, wide field of view instrumentation in gamma-ray astronomy is currently limited
to the northern hemisphere and hence, lacks sensitivity to our Galactic Center and the rest of the southern sky. A Southern Gamma Observatory comprising an array of ground-level detector units with a high fill factor (> 70 %) at high altitude (> 4 km) could be used to observe the southern sky. Water Cherenkov Detectors (WCDs) have shown their potential as detector units for such an array. Detailed simulations are needed to understand the response of WCDs to the flux of secondary particles impinging on them. In this contribution, we study the complete simulation chain from the air shower simulation with CORSIKA to the detector level simulation with GEANT4, in an attempt to optimize WCDs.