Once started, the device automatically shuts off after 8 hours, restarting at the same time the next day - 8 hours on, 16 hours off. No water needed as it contains natural essential oils that diffuse into a mist through microscopic holes in the vibrating plate. Battery operated for placement anywhere. Each refill lasts up to 45 days on the lowest intensity setting. Batteries included.Package Includes: (1) Diffuser; (1) Refill; (3) AA Batteries