To provide a device which does not necessitate stirring and driving, makes service water flow by a simple configuration, prevents denaturalization of service water due to the stay of water for a long time, and supply water having good quality easily and stably.

A liquid level sensor which detects water level position of service water 7 which is collected it provided in an upper part of a water storage tank 4 which has low light transmission property and is hollow and substratially cubic. A supply pipe 11 which makes service flow by a pump is connected to the water storage tank 4, and a nozzle means 12 is connected to a lower end part of the supply pipe 11. The nozzle means 12 is constituted in such a manner that one of a pair of side plates 13, 13 which oppose mutually is tilted toward the other side plate 13 so that its width becomes small and that a thin and long injection port 14 is opened and formed in the vertical direction on one end face having small width. The nozzle means 12 is arranged at a lower position than the lowest position of water level in such a manner that the direction of ejection of service water 7 is set to abut 30 degrees in the clockwise direction for an inner wall face of the water storage tank 4. Service water 7 which jets acts efficiently on the clockwise flow in the same direction as the direction of rotation which corresponds to the rotation of the earth in the northern hemisphere, and it is possible to maintain its flow for many hours and prevent charge of water quality.