Most cruise lines will allow you to bring a reasonable amount of water/soda on board with you. I searched the NCL website and found this:
What can't I bring onboard?
Passenger is not allowed to bring on board the vessel without the previous written permission of the Carrier any intoxicating liquors, or beverages, firearms, weapons of any kind, ammunition, explosive substances or any goods of a dangerous nature, nor animals of any kind, except service or guide animals, provided the passenger notifies Carrier prior to the cruise of his intention to bring such animal and agrees to take sole responsibility for any expense, damage, injuries or losses associated with or caused by such animal.
I'm not sure how to interpret the statement "liquors, or beverages", but I take that to read intoxicating beverages....so you should be fine with water/soda.
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