Maybe there’s other planets with water out there, eh? Interesting question but there is no need to go to all that trouble as far as we here on Earth are concerned. As someone else pointed out, Earth’s orbit is fairly stable and the earth already cleared a path around the sun, absorbing all the debris in our area as it went around and around.
How much water are we talking about, anyway? Let’s see. The amount of water including all the fresh water and all the oceans on Earth is very small compared to the size of the Earth. Therefore we know that not a very high percentage of icy comets were needed to produce water, and we also suspect that chemical reactions also produced water. This image illustrates the amount of water compared to the size of the earth.
So as you can see from the above image, Earth really is mostly solid. There’s really not that much water in comparison.
In conclusion, we didn’t need a lot of icy comets percentage wise to produce this effect.