The watery portion (the water of the Causal Ocean) is beyond the sevenfold coverings (of the universe), and each covering is ten times more expansive than the previous covering
SB Canto 2
After reaching Satyaloka, the devotee is specifically able to be incorporated fearlessly by the subtle body in an identity similar to that of the gross body, and one after another he gradually attains stages of existence from earthly to watery, fiery, glowing and airy, until he reaches the ethereal stage.
Anyone who can reach Brahmaloka, or Satyaloka, by dint of spiritual perfection and practice is qualified to attain three different types of perfection. One who has attained a specific planet by dint of pious activities attains places in terms of his comparative pious activities. One who has attained the place by dint of virāṭ or Hiraṇyagarbha worship is liberated along with the liberation of Brahmā. But one who attains the place by dint of devotional service is specifically mentioned here, in relation to how he can penetrate into the different coverings of the universe and thus ultimately disclose his spiritual identity in the absolute atmosphere of supreme existence.
According to Śrīla Jīva Gosvāmī, all the universes are clustered together up and down, and each and every one of them is separately sevenfold-covered. The watery portion is beyond the sevenfold coverings, and each covering is ten times more expansive than the previous covering. The Personality of Godhead who creates all such universes by His breathing period lies above the cluster of the universes. The water of the Causal Ocean is differently situated than the covering water of the universe. The water that serves as covering for the universe is material, whereas the water of the Causal Ocean is spiritual. As such, the watery covering mentioned herein is considered to be the false egoistic covering of all living entities, and the gradual process of liberation from the material coverings, one after another, as mentioned herein, is the gradual process of being liberated from false egoistic conceptions of the material gross body, and then being absorbed in the identification of the subtle body till the attainment of the pure spiritual body in the absolute realm of the kingdom of God.
Śrīla Śrīdhara Svāmī confirms that a part of the material nature, after being initiated by the Lord, is known as the mahat-tattva. A fractional portion of the mahat-tattva is called the false ego. A portion of the ego is the vibration of sound, and a portion of sound is atmospheric air. A portion of the airy atmosphere is turned into forms, and the forms constitute the power of electricity or heat. Heat produces the smell of the aroma of the earth, and the gross earth is produced by such aroma. And all these combined together constitute the cosmic phenomenon. The extent of the cosmic phenomenon is calculated to be diametrically (both ways) four billion miles. Then the coverings of the universe begin. The first stratum of the covering is calculated to extend eighty million miles, and the subsequent coverings of the universe are respectively of fire, effulgence, air and ether, one after another, each extending ten times further than the previous. The fearless devotee of the Lord penetrates each one of them and ultimately reaches the absolute atmosphere where everything is of one and the same spiritual identity. Then the devotee enters one of the Vaikuṇṭha planets, where he assumes exactly the same form as the Lord and engages in the loving transcendental service of the Lord. That is the highest perfection of devotional life. Beyond this there is nothing to be desired or achieved by the perfect yogī.