Abstract: A precise shading model is required to display realistic images. Recently research on global illumination has been widespread. In global illumination, problems of diffuse reflection have been solved fairly well, but some optical problems after specular reflection and refraction still remain. Some natural phenomena stand out in reflected/refracted light from the wave surface of water. Refracted light from water surface converges and diverges, and creates shafts of light due to scattered light from particles. The color of the water is influenced by scattering/absorption effects of water molecules and suspensions. For these effects, the intensity and direction of incident light to particles plays an important role, and it is difficult to calculate them in conventional raytracing because light refracts when passing through waves. Therefore, the pre-processing tracing from light sources is necessary. The method proposed here can effectively calculate optical effects, shafts of light, caustics, and color of the water without such pre-processing by using a scanline Z-buffer and accumulation buffer.