water and math

So Claire's AJ post got me thinking last night about how people are about 70% water.. then I was thinking about all the calculations done for that urine estimate and how it was pretty simple.. so I got curious:

If you could extract all the water out of every person, how much would you have?

So I assumed:

avg volume of water per person = 70% (by weight)
Avg weight of person = 150 lb.

This equals 105 lbs of water.. which when you do the conversion.. 16oz/lb.. 128 oz/gallon gives you 13.125 gallons of water per person.. 6.5 billion people on the planet.. gives 85.3 billion gallons of water.

Now I have this number, but i have no idea how much water 85 billion gallons of water is. So here's where I got a little out of control.

So I thought, how much would sea level rise if you through 85 billion gallons of water into the oceans? So I looked it up:

85 billion gallons of water is about 328 million cubic meters of water.. this is equal to about 0.328 cubic kilometers.. not as much as I was hoping for.. so according to google, the surface area of all the oceans is 327,776,700 square kilometers, which when you do the math leaves us with about 1.0 um rise in sea level. How disappointing. I was really expecting more.

So then I thought, alright what about Oahu? How deep would Oahu be covered? It's a lot smaller than the whole earth..

Surface are of Oahu = 386,500 acres = 1.564 billion square meters divide that by the volume of people water, you find that Oahu would be covered by about 0.21 meters of water, or about 8".

I found this very disappointing as wel (it's been kind of a disappointing morning)l.. but at least it was fun and I got to use that part of my brian which hasn't had to do anything close to math in about 2.5 years. Thoughts??