[S0122017]

Easy: Where else in our solar system do you find enough water to make a popsickle let alone a comet?

Most comets don't come from this solarsystem.

In any case: there is probably plenty of water on Europa, Jupiter to flood the earth several times over. And there are many suspected waterice deposits on other worlds in this solarsystem.

[editor-surveyor]

All comets are from this solar system, and none heve been found that are not orbitally coplanar with the earth and the sun. If you have studied Johannes Keppler's work, then you know that it is unlikely that their origin could have been any place other than earth.