750,000 parts per million = 75% 1,000,000 parts per million = 100%

Did you mean to say 1 part/750K and 1 part/1M ?

No.

75% of the Earth is covered with water.

In any case, my numbers probably too low. I didn't consider regions covered in ice. ;-)

75% of the surface area is covered in water. The volume/mass of the earth is more than just the surface area.

His OP did specify surface area.

Thanks. :-)

And I doubt we'll be digging deeper than 10 feet on the Moon anytime soon.