I've never seen many water bottle filling stations at airports. In some of them, such as Hamburg you have to ask at the bar as there are no water fountains.
That's consistent with my first-hand understanding that Germans are culturally opposed to drinking plain water. You'll never be offered tap water at any restaurant or café, and if you ask for Leitungswasser (tap water, literally "plumbing water"), you'll get an eye-roll or disgusted look, partly because that saves you the cost of a bottle of water.
