water as a symbol of good

[Kuruharan]

The sea is also a menacing body of water; it is the sea which drowns Numenor, and the sea which takes the Elves away from Middle Earth.

I disagree with this, at least in a symbolic sense. The sea is portrayed as being a tool of the Valar. Numenor deserved what it got. I don't find the sea being the means of transporting the Elves to Valinor to be particularly menacing.

Belariand was a slightly different circumstance as it was destroyed by the breaking of Thangorodrim, and then it sank.

Other examples of water being attributed protective qualities:

Boromir being cast adrift in the Great River.

Galadriel uses mists for protective purposes (the ride of Eorl).