Bottled water carries a fee. The no-charge water comes from the ship's potable water tanks, and is perfectly safe to drink. It is what we always drink when cruising.
And as for iced tea - remember that most cruise ship dining rooms are staffed by people from just about everywhere but the U.S.A. Iced tea is quite "foreign" to these folks. Iced tea on a ship has never impressed us - it is either too weak or too strong, and it is never pre-sweetened. But then I prefer it without any sweetener - just a little lemon.
I generally do not recommend that adults buy a soda card. It isn't that good of a deal for them. It is a different story for kids, where the cards are cheaper. A can of soda is typically $1.50 plus 15% for the gratuity.
I have found that if you go to the specialty coffee shops when they are not crowded and ask nicely with a nice tip they will brew you some sweet tea and serve it on ice for you. I am a native north carolinian and I love my sweet tea when its hot. The people on the soverign are always happy to make the guests happy. I tip them 5 dollars cash plus the cost of their specialty tea and I get sweet tea for a couple of days. If you haven't tried the Soverign I do strongly recommend you do.