Dear Lillian,
Carnival places large bottles of water in the cabins ($3.35 each), and makes bottled water available at the ship exits when you are going ashore. Problem is, they DO charge for all bottled water.
We have always brought bottled water on board packed in our luggage. Two weeks ago, we even saw several people in the embarkation line who carried a case (12 or 16 botttles) of water on board. Carnival posts on their website that this is OK. Just carry enough for your group, and it will be fine.
I also had a small collapsabe ice chest that I kept in the room. Mention it to your cabin steward, and slip them a few EXTRA bucks, and they will keep your water iced down for you.
For other free drinks (tea, lemonade, juice, tap water), be sure to bring some sort of closeable, wide-mouth bottle, so you don't have to keep getting out of your deck chair to re-fill those small glasses they provide. (wide-mouth allows you to add ice).
And... this time I brought a travel-style coffee mug to put my hot chocolate or coffee (free. also) in, so I wouldn't spill it while walking around.
Have a great time!