Depends on the countries water quality. Some countries don't have water good for drinking, and others have poor taste which many are put off by. That being said, many EU airports do have water refill machines. Germanys airports for example..

While I understand where you're coming from and that this thinking is probably (and somewhat understandably) why there are no water filling stations, I find this incredibly nasty. I don't want to fill my water bottle in a public restroom riddled with bacteria.

And yes, I'm fully aware that a water filling station will probably be just as nasty, but it's the thought that bugs me.