It's not worth the hassle...We brought our own water on the Miracle last year and found that it wasn't worth the effort. The ship's water is fine to drink, plus they had bottled water available for purchase to bring ashore while on excursions. I don't remember what they charged, but I remember that it wasn't that expensive at all. So reasonable that we decided that we would not bring our own on future trips...
PS We're on the Destiny 7/1 with an 11 y/o. Please let me know how your trip goes and what you'd recommend since you're traveling with kids as well.