My husband uses a CPAP. He carries it onboard in its bag, with an extension cord inside. As Dwayne mentioned, be sure that the extension cord is in good condition. Also be prepared to remove the CPAP from its bag for a secondary security examination. Doesn't happen all the time, but more often than not in our experience.
Some cruise lines will provide distilled water (for a fee) if requested far enough in advance. This is done through the Special Needs department. We've found it easier to just bring it onboard ourselves. It will need to be in your carry-on when you board the ship. If you are also flying, put the bottle in checked luggage, then move it to your carry-on when you retrieve your luggage after your flight. We always bring a new, sealed bottle so that it's not mistaken for something else.