I am just off the Rotterdam in March. I did not have any issue waiting for coffee, water, tea or lemonade in the Lido for breakfast, lunch or dinner. We ate a few times in the dining room and, again, I haver had an issue waiting for my wine to be delivered.
There are bars you can walk up and order a drink at various places throughout the ship, which you can take with you, I found myself doing that a few times, just because I was there and figured I'd get it.
We had the Have it All Package, I would get a few cans of soda or water's for my cabin, so I had them readily available.
Don't sweat the small stuff, it all works out, go and enjoy the Rotterdam, she's a beautiful ship with an amazing crew, she's one of my favorites.