Using the equation for the volume of a sphere, this comes out to a radius of about 683 km. Converting to miles, 424. Converting to diameter, 848. Knowing some typical distances across country (I drive a lot) the size of the water sphere looks about right.
For even more fun (yeah, I know, twisted). I decided to see if ignoring "us" as a water store is valid. 7 billion people, average maybe 150 lbs each, 70% of that is water... Some conversions from lbs to cubic ft to cubic km... All of us humans, collectively account for just 0.33 cubic km of water. Compared to the 1.35 billion cubic km in the oceans. Ok, we don't count. What about the other stuff? Well, what if my assumption is wrong, say the oceans only account for 90% of the water. Running the numbers again gives a sphere with a diameter of 879 miles instead of 848. Well, at the scale of the picture, I can't tell a difference of 31 miles. Fun stuff. Interesting picture.
If it weren’t for the fact that their ignorance is contagious it would be amusing that today’s so called eco warriors have about as much understanding of science as the priests who interrogated Galileo. They don’t understand that water on this planet is never “lost”. Or that human “produced” CO2 will be taken up and converted back into Oxygen and Carbon by living vegetation. Every element of this planet is in a cycle, forming and reforming into different molecules and stages of gas, liquid, and solid. We are just very temporarily beneficiaries and observers of these cycles, until the day all the stuff we’re made of gets thrown into the same thresher.