The invention discloses a layered structure of a water storage device. The layered structure comprises a water tank. The lower portion of the water tank is connected with a top plate of a mixing box.A liquid level detector is arranged on one side plate of the mixing box. A drainage opening is formed in the other side plate of the mixing box. The drainage opening is connected with a vehicle washing brush head through a pipeline. The water tank is composed of a tap water cavity and an adding cavity. The tap water cavity delivers tap water to the mixing box. The liquid level detector collects tap water liquid level information and sends the tap water liquid level information to a controller. The controller controls a driving device to be started according to the tap water liquid level information. The adding cavity internally comprises a hose. The hose is connected with a metering device, the driving device and a probe in sequence. The probe enters the interior of a washing agent bottlethrough a cap opening of the washing agent bottle. The driving device is controlled by a processor. The metering device collects flow information of the hose. When the flow information is matched withthe tap water liquid level information, the processor controls the driving device to be stopped. The controller adopts a single chip microcomputer or a PLC.