PURPOSE: To ensure a sanitary safety with a flowout eliminated of harmful object, by constructing the tank wall of reservoir into two layers, where the inner side to be contacted to water is applied a synthetic resin with colored pigment not used and the outer side formed into a colored layer with the pigment used completely not penetrating the sunlight.

CONSTITUTION: For the construction of a water reservoir 1, an inner layer 3 to be contacted to water is made by using a non-colored synthetic resin safe for food sanitation, for instance, polyethylenes, and an outer layer 5 is formed by using a colored synthetic resin with a pigment applied completely blocking the sunlight. And on said water reservoir 1 is capped a storage plate 7 the surroundings of which are fixed by bolts, and on top of this is mounted an automatic pump 11 being installed by bolts. In such construction of the tank wall of the water reservoir 1, any evidence of flowout is provided from the inner layer 3 even after a long time contact to water, further with a disinfectant bleaching powder not disappearing because of a perfect blocking of the sunlight made by the outer layer 5, thus a sanitary safety can be ensured.