It's a case of bottled water delivered to your stateroom for about $36 including the tip.
Options--drink the ship's water. It is safe and tastes good. Get a case of water on the way to the port if you will have either a rental car or a towncar service (far less costly!) We bring an empty bottle for each person when we fly. It can be refilled for excursions.
We've found that in port, the farther you get from the ship the cheaper the water gets. As you leave the port area, $3 per bottle is not unusual. It has been $1 a short walk farther.