Where did the earths surface water come from?

Explanation:

There are two dominant theories:

The inside-out model proposes that the Earth formed with trace amounts of water structurally bonded to the minerals in the mantle. This water makes its way to the Earth’s surface through volcanic processes.  

The outside-in model proposes that the Earth formed without water, which came with other volatiles from the meteorites or comets that bombarded the young planet. This water was probably mixed into the upper layers of the Earth and was later brought to the surface through volcanism.