Why not "unseres Wasser"?
In acusative, (m) unseren, (f) unsere, (n) unser. Here: das Wasser (n) and thus, unser Wasser.
mm I think its because we have a nominative pronoun here and Wasser is neutral, so unser is right. Correct me if im wrong please!
Yeah, unser doesn't take -es in mixed declension
Ich trinke deinen Milkshake.