Using the values you supplied I get 0.12% H20 for a comet. Would you like to take a stab at what percentage of he Earth is ocean? 0.11%. Looks like the Earth is a big ol' comet.
Assuming these numbers are correct, it seems to imply that rocky bodies, when they formed out of the cloud around our protosun, contained about .12% water. Which doesn't sound too hard to believe to me, so much of the water in our planet probably was there to begin with.