Earth may have underground 'ocean' three times that on surface

[Anomalocaris]

All water on earth did come from comets, and there is nothing magical about these comets. The comets which brought water to earth are all, as far as we know, normal run of the mill comets.

Is there any consensus opinion on where the water in comets came from?
And why they are so watery rather than rocky?

I ask as someone profoundly astro-geologically ignorant.
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Comets are actually partly rocky. They are actually a mixture of water ice, rocky material, and carbonaceous material.

The water in the comets came from the original nebula from which the whole solar system formed. We can confirm through direct mseasurement nebulas in which active star formation are happening now are all high in water molecule content. So we believe the nebula in which the sun formed was high in water content too.