The present invention provides a gas water bottle adaptor that is suitable for attachment to a water bottle and to a bottle cap. The adaptor can include a gas inlet on one side thereof suitable for attachment to the gas connection of an endoscope. A sealing member can be affixed to the adaptor to prevent leakage of any fluid (e.g., liquid or gas) that is inside of the water bottle. The adaptor may be used in endoscopy methods and is particularly useful for adding a secondary gas source to a water bottle.