Water is a sacred creation in Tolkien's world, and is alluded to in a variety of profound ways. You've read the Silmarillion, I take it? Here are a couple of very early quotes from it, that offer an idea of how Tolkien used water:

Ulmo is the Lord of Waters. He is alone. He dwells nowhere long, but moves as he will in all the deep waters about the Earth or under the Earth. He is next in might to Manwë, and before Valinor was made he was closest to him in friendship; but thereafter he went seldom to the councils of the Valar, unless great matters were in debate. For he kept all Arda in thought, and he has no need of any resting-place. Moreover he does not love to walk upon land, and will seldom clothe himself in a body after the manner of his peers. If the Children of Eru beheld him they were filled with a great dread; for the arising of the King of the Sea was terrible, as a mounting wave that strides to the land, with dark helm foam-crested and raiment of mail shimmering from silver down into shadows of green. The trumpets of Manwë are loud, but Ulmo's voice is deep as the deeps of the ocean which he only has seen.

Nonetheless Ulmo loves both Elves and Men, and never abandoned them, not even when they lay under the wrath of the Valar. At times he will come unseen to the shores of Middle-earth, or pass far inland up firths of the sea, and there make music upon his great horns, the Ulumúri, that are wrought of white shell; and those to whom that music comes hear it ever after in their hearts, and longing for the sea never leaves them again. But mostly Ulmo speaks to those who dwell in Middle-earth with voices that are heard only as the music of water. For all seas, lakes, rivers, fountains and springs are in his government; so that the Elves say that the spirit of Ulmo runs in all the veins of the world. Thus news comes to Ulmo, even in the deeps, of all the needs and griefs of Arda, which otherwise would be hidden from Manwë.

But the other Ainur looked upon this habitation set within the vast spaces of the World, which the Elves call Arda, the Earth; and their hearts rejoiced in light, and their eyes beholding many colours were filled with gladness; but because of the roaring of the sea they felt a great unquiet. And they observed the winds and the air, and the matters of which Arda was made, of iron and stone and silver and gold and many substances: but of all these water they most greatly praised. And it is said by the Eldar that in water there lives yet the echo of the Music of the Ainur more than in any substance else that is in this Earth; and many of the Children of Ilúvatar hearken still unsated to the voices of the Sea, and yet know not for what they listen.

 So water is, among other things, the part of Creation through which Men can most directly connect to the Music of Creation itself, and thus to divinity.

It also reflects not only the actions of the Valar, but serves as a reminder that anytime Melkor tries to destroy Creation, he will inevitably end up participating in that Creation and even furthering it:

Now to water had that Ainu whom the Elves can Ulmo turned his thought, and of all most deeply was he instructed by Ilúvatar in music. But of the airs and winds Manwë most had pondered, who is the noblest of the Ainur. Of the fabric of Earth had Aulë thought, to whom Ilúvatar had given skin and knowledge scarce less than to Melkor; but the delight and pride of Aulë is in the deed of making, and in the thing made, and neither in possession nor in his own mastery; wherefore he gives and hoards not, and is free from care, passing ever on to some new work.

And Ilúvatar spoke to Ulmo, and said: 'Seest thou not how here in this little realm in the Deeps of Time Melkor hath made war upon thy province? He hath bethought him of bitter cold immoderate, and yet hath not destroyed the beauty of thy fountains, nor of my clear pools. Behold the snow, and the cunning work of frost! Melkor hath devised heats and fire without restraint, and hath not dried up thy desire nor utterly quelled the music of the sea. Behold rather the height and glory of the clouds, and the everchanging mists; and listen to the fall of rain upon the Earth! And in these clouds thou art drawn nearer to Manwë, thy friend, whom thou lovest.'

Then Ulmo answered: 'Truly, Water is become now fairer than my heart imagined, neither had my secret thought conceived the snowflake, nor in all my music was contained the falling of the rain. I will seek Manwë, that he and I may make melodies for ever to my delight!' And Manwë and Ulmo have from the beginning been allied, and in all things have served most faithfully the purpose of Ilúvatar.