If the earth was once molten, where did water come from?

Question: If the earth was once molten, where did water come from?
- Keywords:
  earth,
  life,
  planet
Asked by Zealousy to Susan, Chris on 18 Jun 2015.
- Susan Cartwright answered on 18 Jun 2015:
  
  We believe it was delivered by comets hitting the Earth after it had solidified. Comets are mostly water. Some might also have come from volcanoes: many minerals incorporate water molecules as part of their structure, and these would have survived the molten stage.

Question: If the earth was once molten, where did water come from?