I am faced with a water dilemma myself now. I usually take a 12 pack of shrink wrapped spring water bottles and check them. Carnival now says I have to carry them on board. I'm thinking of just opening the case and showing them when I check the luggage what they are and see what they say. Hey, that is a lot to lug on board. If they say no, that is fine and I'll lug them on.
I have to have my spring water because the ship's water doesn't agree with me for some reason. Others say it is fine with them. I drink a lot of water and try to limit it to tea and ice on board.