A photocatalytic water-processing system decomposes organic and inorganic materials present in water. The system includes a reservoir for storing the water to be processed, a main unit formed separately and connected to the reservoir, an inlet pipe for guiding the water from the reservoir to the main unit, an outlet pipe for returning the water to the reservoir, and a pump for guiding the water from the reservoir to the main unit and returning the water. The reservoir has an electrode unit therein for electrolyzing the water so as to flocculate and precipitate the inorganic materials in the reservoir, and a filter is arranged within the main unit. Also, a photocatalytic processing device is arranged within the main unit at a downstream side of the filter for decomposing the organic material in the absence of scale formed of the inorganic materials.