isn't it "en vann?" Is it an exception where it because a word iwth a "et" suffix? I know "barnet" is both, so is it?
There are no nouns which changes gender in Norwegian as you decline them. There are only a handful with multiple genders, but they are rare, and even if they can have different genders, you should never mix them as you decline them. So unlike Spanish, there is no 'el agua, las aguas' in Norwegian.
en/et øl (a beer) - These have different meanings.
en/et/ei gardin (a curtain) - These have the same meaning.
I'm not sure I understand. "Barn" is a neuter noun. "Et barn" is "a child" and "barnet" means "the child." "Vann" is also neuter. "Vannet" means "the water."