Well, as we have cruised 3 times this year with the SBP, I think I have an idea on how it works. I know the water from the tap is just fine, and the water cans can be refilled form the tap. So if I was worried about 15 drinks, I would be refilling a water can a couple of times, rather than getting 6 cans of water per day. Plus, if you need water (like I do, as a kidney stone deterrent, and after workouts), its available at all meals and dining locations, free.