In case you missed it, today Carnival changed their policy and is now forbidding people from bringing water onto the ships and instead making people buy it from them or drink the tap water.
Thankfully though, there's an awesome product that I'll be taking with me the next time I cruise and that's the Zero Water Tumbler. For the past week or so I've been testing it out using San Diego tap water and it's been producing the same high quality of filtration that I experience in the full-sized pitchers but it is portable and convenient. Even if you don't cruise, this is a great item to keep with you in your backpack since you really shouldn't be using bottled water anyhow since it is pretty bad for the environment.