This is a valid explanation for the formation of ice in the outer solar system past the snow line (and is especially applicable to the formation of Uranus and Neptune), but it does not explain the formation of water on the Earth. Past the snow line, water will not condense out of intrastellar hydrogen and oxygen gas. In fact, it will be blown out past the snow line by radiation pressure and the solar wind. Additionally, the impact rate during the formation of the Earth would have stripped the early atmosphere. The formation of water on the Earth is probably due to comet impacts when protoplanetary formation was complete. This really shouldn't be that surprising to people. The impact rate in the inner solar system is much higher than the outer solar system and the impact rate was much higher during the formation of the solar system.
Intuitively most people will probably look at the Moon to see how many impact we would have had. Of course this would be misleading since the Moon obscures impacts (by dust or lava flows) and since the Moon would have a lower impact per unit of surface area due to its lower gravitational field. A closer example might be a little less than the impacts shown on Mercury. These impacts would easily have deposited a large ocean on the Earth. While people like to think that the Earth has a lot of water, compared to the total mass of the planet it is trivial. If you take a basketball and dip in in water and then shake it off, you will have more water in proportion than the Earth does. All of the water on the Earth accounts for 0.02% of the mass of the planet. In the case of the basketball example (600 g), that would be 120 mg of water (about 5 droplets of water).
The water would have been formed after the Snova and during the solar system's formation. During the initial condensation the temperature would have been up and heat would have been released. Free water certainly wouldn't remain on hot rock and bound water would have been absent earlier.
"Past the snow line, water will not condense out of intrastellar hydrogen and oxygen gas."
The formation of water is a reaction, not a condensation. It requires an activation energy that would have been provided by the temps the after cooling of the Snova remnants and the during solar system formation.
"In fact, it will be blown out past the snow line by radiation pressure and the solar wind. Additionally, the impact rate during the formation of the Earth would have stripped the early atmosphere. The formation of water on the Earth is probably due to comet impacts when protoplanetary formation was complete."
The water would still be contained by the solar system's gravitational field and would condense with itself and other cooler objects in both the interplanetary space and those with eccentric orbits that would cause then to leave the solar system for periods of time. As those objects travel through space, they would collect more water. Once the Earth's surface was less than 100oC, free water would collect on the sphere.
I think the mass percentage of water is more like 0.04%,and some of that's bound water in rock. The mass ratio is misleading though. The planet is mostly Ni and Fe, so a volume ratio is a better. Very roughly, the molar ratio would be about 3 and the density ratio about 8. So the volume ratio would be up to ~0.33%.
