You can also get water, free of charge, any time up on deck 9 by the Mickey Pool. It's not bottled water, but it tastes pretty good. You can also order the following package from room service:
MINI BAR: Your bar can be stocked with the following selections (15% service charge applied to all beverage deliveries: Package 1 (6 soft drinks, Coca Cola products, $7.50); Package 2 (6 domestic beers, $15 or 6 imported beers, $18); Package 3 (3 soft drinks, 3 domestic beers, 3 bottled waters, sparkling or non-sparkling, $15.75, or $17.25 with imported beers).
I would recommend bringing bottled water on-board with you if you really want bottled water. If you like ti cold, then you'll need to put it over ice or put the bottled water right in your ice bucket which your stateroom attendant will refill every morning and night if you need it. The cooler boxes in the staterooms are just that. They aren't refrigerators, they're coolers.