The waters are goddesses in the Rigveda and they are addressed in the plural, always. The hymns to them are short, and what they ask for is not abstract: the waters are asked for a share of their pleasantness, for medicine, for long sight, for the removal of whatever the speaker has done wrong. Two ideas run through them and neither has been improved on since. The waters are mothers, meaning that everything comes out of them and that they are the first thing that was there. And the waters carry, meaning that what is put into them goes away.
The second idea is the one that made the whole of the later ritual system possible. A defilement, in this way of thinking, is not a state of mind and not a legal condition. It is a thing on a person, and a thing on a person can be moved onto something else and taken off downstream. That is why the waters are asked to remove the false oath, the curse, the offence against a friend, and it is why washing is a religious act rather than a hygienic preliminary to one.
They keep good company. Varuna, whose business is the moral order and the bonds it imposes, dwells in the waters. Agni has a form called the child of the waters, fire inside them, which is a paradox the poets enjoy rather than resolve. Soma is pressed and mixed with them. The waters are not a department of the pantheon so much as the medium the rest of it works in, which is a status hard to hold and hard to lose, and they never lost it.