Semiconductor-based photocatalytic processes for removing hazardous chemicals from contaminated water have been studied for nearly 20 years. One goal of this research is to use the sun as the light source. This article assesses the state of development of solar heterogeneous photocatalytic processes for treating contaminated water and identifies key barriers that must be overcome for the technology to achieve commercial success. Some industry members estimate that the cost of using solar technology for waste treatment will need to be less than half the cost of a ＇＇conventional＇＇ technology in order to gain market acceptance. The number of applications that are near commercial viability could be expanded with significant progress in the improvement of the photo-efficiency of the photocatalytic process.