Abstract: The appearance of many natural materials is largely influenced by the environment in which they are situated. Capturing the effect of environmental factors is essential for producing realistic synthetic images. This work models the changes of appearance due to one such environmental factor, the presence of water and other liquids. Water affects the interaction of light with a material, both on the surface and in the interior. We model both of these effects inside of a physically-base sub-surface scattering simulation, implemented in a general Monte Carlo ray tracer. We exercise our methods with a variety of example scenes, demonstrating many characteristic changes of appearance due to water.