The Earth's atmosphere does not contain a large amount of water. Its estimated volume of water is about 3,100 cubic miles (12,900 cubic kilometers), which is roughly just 0.001% of all of the water on Earth. In fact, if all of the water in the atmosphere was released at one time, it would equal only about 1 inch (2.54 cm) of the world's oceans' depth. The atmosphere’s function with water is more transportation rather than storage. As water evaporates, it converts to vapor, which then moves into the atmosphere. Once there, the vapor condenses into clouds, which then release the water as precipitation to get back to the Earth’s surface.
More about water in the atmosphere: