The Brahmaja cloud is born from the breath of Brahma. These clouds are created when thunder and lightning proceed. Pakshaja are the clouds which were originally the wings of the mountains, and which were cut off by Indra. These clouds are the largest of all and at the end of the Kalpas and Yugas, they pour down the waters of the deluge.
The shell of Lord Brahma or of the universe is said to be formed by the primitive clouds. As per the Vishnu Purana, during eight months of the year the sun attracts the waters and then pours them upon earth as rain.
Consequently, the Linga Purana describes that there is no waste of water in the universe as it is in constant circulation. The Vishnu Purana adds, "The water that the sun has drawn up from the Ganga of the skies he quickly pours down with his rays, and without a cloud; and men who are touched by this pure rain are cleansed from the soil of sin and never see hell: this is termed celestial ablution."
As per the Vishnu Purana, the water which the clouds shed upon the earth is the Ambrosia of living beings, for it gives fertility to the plants which are the support of their existence.