Abstract: Water drops and water flows exhibit interesting motion behaviors and amazing patterns on the surfaces of objects, such as leaves of plants and glass panes. Water drops and water flows are commonly seen in a rainy day. A water drop contains a small amount of water. The motion of a water drop is affected by various factors, including gravity, surface tension, cohesion force and adhesion [Zhang et al. 2012]. The situation is more complicated when we consider the roughness of the surface, surface purities and etc. Kaneda et al. [1993] proposed a discrete model of a glass plate for simulating the streams from the water droplets. The glass plate is divided into a grid. A water droplet is represented as a particle. The law of conservation of momentum is applied for merging droplets. A simple ray tracing technique is adopted for rendering the water droplets that are represented as spheres.