It is quite understandable to query about how the Earth gets water. But if you like to delve deep into it, then you will see that my Natural Blasting theory is the prime reason for it. The reason is that when the Earth was born 4.5 billion years ago, then the atmosphere of the Earth was so hot and not conducive for the creating any kind of the life-producing process. Therefore, Earth was forming from the highly gaseous material to a substantial one. But in the initial stage of Earth birth, it was not possible for the Earth to make any kind of chemical processing for the life development as well. Actually, at this stage, the Earth itself was highly unstable and it was going to the unpredictable future.
Even, at this stage, a favorable atmosphere is unlikely possible. So the Earth itself waited for a couple of million years for the stable atmosphere. After the stability in the Earth, atmosphere was started to take its own course, then the life producing gaseous substance like oxygen, hydrogen, methane, nitrogen and other gaseous stuffs was rising in the Earth atmosphere at an alarming rate. But at this time, one problem was started to appear in the Earth atmosphere. It was the filling of gases in the Earth atmosphere at high density which was very much dangerous for the younger Earth as well. But somehow it was necessary to minimize its gaseous pressure in the atmosphere of the Earth.
Even, at that time, the land masses were not developing. So the immediate need for the release of excessive gaseous material from the Earth environment was required. Therefore, the Natural Blasting was occurred at that time. It is made a kind of situation which was conducive for starting a chemical reaction with hydrogen and oxygen gases in the Earth atmosphere. Because the proportion of oxygen and hydrogen gases in the Earth atmosphere was in an enormous proportion which was larger than another gaseous material at that time. Therefore, these gases had the maximum numbers of particles in the Earth atmosphere which was compelled to happen certain excitement over the times for making water in this planet.
So that the Natural Blasting ignites the chemical process between oxygen and hydrogen for making the water molecules. Practically, this process happened due to the natural electrical striking which occurred through the bombardment of comets and asteroids in the Earth atmosphere at the regular interval. It was continued for the million years as well. But you should never think that the continuous bombardment of asteroid or comets would bring water from the outer space. Rather, it was happened due to the Natural Blasting in the Earth itself.
If you look at this assumption, then you will see that a 2-miles long asteroid or comet will never have any potential to cover up the Earth with water. Even, if it continues to strike the Earth at the several times. Actually, the scientists have no any concrete evidence of it as far as my knowledge is concerned. Therefore, it is sure that the Earth gets water through the Natural Blasting mechanism without any doubt as well.
N.B. This article is dedicated to my science guru, late Sir Arthur Charles Clarke.