Abstract: A purified water storage device includes a container including a cover, a bladder having a top secured to the cover and a bottom secured to a through hole of the container, a pipe for both venting and draining having an end connected to the bladder and communicating therewith, the pipe including a check valve, a water pipe having an end connected to the bottom of the bladder and communicating therewith, and a level sensor disposed externally of the container and having an end connected to the bottom of the bladder and communicating therewith. The watertight bladder is made of thermoplastic for medical or food purposes. The bladder can be replaced after a predetermined times of use rather than regular cleaning. Venting is carried out and overflow is prevented. The device has the same effect as an open container. Its material is safe and cleanness can be maintained.