To store a large quantity of city water even during usual water supplying, by parallelly and vertically installing water reservoir cylinders and providing the water inlet in the lowermost water reservoir cylinder and also providing the water outlet in the uppermost water reservoir cylinder.

A plurality of water reservoir cylinders 2 are parallelly and vertically arranged in a drinking water tank. The water inlet 5a is provided in the lowermost water reservoir cylinder and the water outlet 9a is provided in the uppermost water reservoir cylinder. This drinking water tank is installed under a sink or the like in a kitchen and a city water faucet is connected to a stop valve 7 through a pipe. City water flows from the lowermost water reservoir cylinder 2 to the uppermost water reservoir cylinder 2 through a check valve 6 and a water inlet member 5 and it is held therein by opening the faucet. In a suspension case of water supply resulting from a disaster, the water supply pressure through the stop valve 7 is reduced and the check valve 6 is automatically closed to prevent water from backflowing from respective water reservoir cylinders to the city water faucet side. Accordingly, water in the cylinders is retained without leakage.