Simulation of Water Cerenkov Detectors Using {\sc geant4}
  We present a detailed simulation of the performance of water Cerenkov detectors suitable for use in the Pierre Auger Observatory. Using {\sc geant4}, a flexible object-oriented simulation program, including all known physics processes, has been developed. The program also allows interactive visualization, and can easily be modified for any experimental setup. 
L. A. Anchordoqui, T. P. McCauley, T. Paul, S. Reucroft, J. D. Swain,   and L. Taylor