Abstract: Recent years have seen increasing research in perceptually-driven reductions in the costs of realistically rendered imagery. Water is complex and recognizable, and continues to be in the forefront of research. However, the contribution of individual lighting phenomena to the perceived realism of virtual water has not been addressed. All these phenomena have costs associated with their rendering, but does the visual benefit outweigh these costs? This study investigates the human perception of various illumination components found in water-rich virtual environments. The investigation uses a traditional psychophysical analysis to examine viewer perception of these lighting phenomena as they relate to the rendering cost, and ultimately reveals common trends in perceptual value. Five different scenes with a wide range of water and lighting dynamics were tested for perceptual value by one hundred participants. Our results provide an importance comparison for lighting phenomena in the rendering of water, and cost reductions can be made with little or no effect on the perceived quality of the imagery if viewed in a scenario similar to our testing.