Is it accurate to compare comets to clouds and rain?
Dating cometary material is tricky, just because you have to go to space to get it. But the dates from the "stardust" mission show that comets are very very old. As old as the oldest asteroids, and date back to the origin of the solar system.

Now while there is evidence that material that formed in the inner solar system when the sun was young, and the planets still forming, was carried to the outer solar system. There is no suggestion that this process is ongoing. There is no astrononomical water cycle.

Although the planets might lose a little water to solar wind. It is very very little. Earth is protected by a magnetic field. Mars has lost all its  water already, as has Venus, and Mercury probably never had much.