How much water is on Earth?
All the water on earth would fit into the sphere shown here
USGS/Jack Cook, Woods Hole Oceanographic
The U.S. Geological Survey has a great illustration on its web site that shows the total volume of all the water on earth — fresh, salt, water vapor, water in ice caps, everything. The entirety of water would make up a sphere with a diameter of 860 miles, or about the distance from Salt Lake City, Utah to Topeka, Kansas. That's a big sphere, but it does show how relatively shallow the oceans are in relation to the earth's diameter. Of course, for voyaging boats, the most important thing is that there is always at least a few inches of water under your keel!