The bottled water sold onboard is Dasani....used to be Zephyrhills. It costs about $1.50 $2.00 per bottle. They sell it at all the bars and usually have stands set up when you disembark at a ports to take along on shore excursions.
The filtered water up at the beverage station is excellent tasting. I usually hate "tap" water, but this water is very good. We also brought along a chuggables water water with a wide mouth and would constantly fill it with ice and water from the beverage station. I saw no reason to spend per bottle for water.
MJ