Sorry - there is no reason why you medically need SODA. No - that is not an ADA violation. Even for diabetics - there are other options available for quick acting sugar sources. Glucose tabs, skittles, you can even get orange juice from the dining room and put it in your fridge in case you need it during the night. We often brought food/beverages to our rooms. You can even get a beverage package that includes soda if you feel you need soda in particular.
Regarding CPAP. Yes - distilled water is recommended for extending the life of the CPAP (hardwater mineral buildup needs to be avoided) - but technically - you can put ANY water in the machine. OR - not use water at all. Personally - I often didn't fill my humidifier. When I travelled with it - I used whatever bottled water I could get my hands on. And when I bought a travel size CPAP for hiking trips - I bought one that used humidification disks instead of water. My point is - There are other options.
As for tap water - that should be use as a last resort due to possible contamination - however - as a last resort - it can be used. I have used it myself as a last result. BUT - only in places where they have "clean" water. I wouldn't risk it in lots of places.
THAT said - sounds like Norwegian offers distilled water for CPAPs.... so no problems there. But if they didn't - they might operate similarly to airplanes - where you can get medical certification for the need of distilled water and carry it on a plane with you. However- always check with TSA/Airlines and Cruiselines directly instead of relying on people you don't know on public forums.