We were on Viking River two months ago and I can confirm that there are always water bottles available, but soda only during meals. There is a table set up by the main desk which is always filled with water bottles for you to bring on excursions or back to your room. In addition, there are two glass water bottles in the rooms which are always refilled/replaced as needed. If you stay in a Veranda Suite they will also stock your in room fridge with soda and other drinks, but I'm not sure if that's the case for the other room categories. Maybe someone else can weigh in, but you're definitely fine with water - there's plenty of that!