Rayvn. Doesn't make sense to me. Of course if you have to drink bottled water for some reason at home, I guess it is the thing to do. Expensive onboard. And the bottle you find waiting on your cabin dresser is not free.
Ship's water is just fine. I've been cruising for 41 years and it hasn't made me sick yet. Tell your cabin steward that you don't want the bottled water and he will keep you supplied with carafe's of water and buckets of ice.
You won't need bottled water aboard ship ever. I believe people are referring to going ashore or heading out for a day at the beach or shore excursion. If at all possible, buy it in town. Otherwise, take it from the ship -- a large bottle of Evian is around $2.00...
Ann is correct. I never buy the bottles of water for sale on the ship. Just bring your own personal water bottle, fill it with ice and water from your cabin for use in warm destinations or on tours or while lounging at the pool or exercising, etc. Every ship I have been on has the best purified water available for you.
I agree with al that has been posted. Don't bring you own, too and takes up too much room . One thing, the bottle water prices are very high! If you really want it, buy on shore. All lines seem too always have it available.....some "push it".