I drink a lot of water rather than soda. Do you have to buy water and can you use a beverage card for it? Is the water that you get out of the tap on a cruise ship drinkable? I'm cruising on Celebrity Summit to Seward in July
Water from the tap on a modern cruise ship is basically distilled water. It will be purer than what you drink at home. Straight from the tap it may be a bit tepid in temperature, but, that is what ice is for. Water is free, even at the bars (at least on any Celebrity ship I've been on).