Emailed my contact at Carnival and here is what I got. Fountain Fun Card pricing.
Also talked with him and he said they are going to start enforcing this on anything found in carry-ons. Key would was Carry-ons
Here is the card information:
Fountain Fun Card
We will offer to all guests the option to purchase a "Fountain Fun Card"
which will allow them unlimited soft drinks for the duration of the cruise
at a one time purchase price (including gratuities). The "Fountain Fun Card"
can be purchased at any bar on board the ship.
In all locations where beverage service is offered, guests may receive a
glass of the soft drink of their choice - one glass will be served at a time
and only to the guest whose name appears on the card. The card cannot be
be used through room service.
Guest Under 21 Years of Age Guests 21 Years of Age and Older