There are two Dominant theories as to the presence of water on earth. The first theory says that Earth was formed ‘dry’ and the water on it came from collision with other celestial objects that had water. The second theory says that the planet Earth was formed ‘wet’ and the water on it existed since the very beginning of the planet. Both theories have their pros and cons.

Then there are also those who reason that the water came from the combination of both the events.