1) You can bring water on board. The only thing is that non-alcoholic beverages brought onboard may not exceed 12 standard (17 oz) cans, bottles or cartons per stateroom. Distilled water or specialized beverages such as, milk for medical purposes, dietary or infant use, are permitted. You are also allow to bring 2 750ml bottles of wine per stateroom.
2) I have never been to St. John’s so I’m not sure but if you get the Shipmate app you can get your questions answer. They have a feature for each port to ask questions to other travelers that have been to that particular port. It’s a great app!