At the U.S. Global Survey website, an image shows all the world's water collected in a sphere, shown floating ominously over the continental U.S. About 860 miles wide, it "includes all of the water in the oceans, ice caps, lakes, rivers, groundwater, atmospheric water, and even the water in you, your dog, and your tomato plant" and would cover most of Alaska. Next to it, a much smaller sphere shows the world's liquid fresh water.
This image shows blue spheres representing relative amounts of Earth's water in comparison to the size of the Earth. Are you surprised that these water spheres look so small? They are only small in relation to the size of the Earth. These images attempt to show three dimensions, so each sphere represents "volume." They show that in comparison to the volume of the globe, the amount of water on the planet is very small. Oceans account for only a "thin film" of water on the surface.
Some fast facts:
About 3,100 mi3 (12,900 km3) of water, mostly in the form of water vapor, is in the atmosphere at any one time. If it all fell as precipitation at once, the Earth would be covered with only about 1 inch of water. The 48 contiguous (lower 48 states) United States receives a total volume of about 4 mi3 (17.7 km3) of precipitation each day. Each day, 280 mi3 (1,170 km3)of water evaporate or transpire into the atmosphere. If all of the world's water was poured on the contiguous United States, it would cover the land to a depth of about 107 miles (145 kilometers).
As a thought experiment, what would happen if all the world's water were assembled into a massive sphere floating over the U.S.? Everything on the planet would be instantly dead, obviously, but perhaps all sorts of things in the water blob would make it (spores, fungus, tardigrades?) and you could contrive some science fictional survivors in the ring of humidity around the sphere at the instant of its creation, coming home from the space station, or something. But surely the blob's formation would be quite a thermodynamic event in its own right? Look, we're going to have to science it out now.
