During the past ten years there has been tremendous research and development in the area of photocatalysis. One of the major applications of this technology is the degradation of organic pollutants in water, by what are called 'advanced oxidation processes' (AOPs). This paper reviews the use of sunlight to produce 'OH radicals for AOPs. The pilot plant-scale systems necessary for performing solar photocatalytic experiments, including the basic pilot plant components and the fundamental parameters related to solar photocatalytic reactions, are described. The paper also summarizes most of the recent research related to solar photocatalytic degradation of water contaminants, and how it could significantly contribute to the treatment of very persistent toxic compounds. It further describes the possibility of using the solar-illuminated photo-Fenton reaction to extend the horizon of solar photocatalysis applications. Various solar reactors for photocatalytic water treatment based mainly on non-concentrating collectors erected during the last few years are also described in detail in the last part of this review.