"I drink water."
Translation:Jeg drikker vand.
Because it's not a specific mass of water (I drink the water), but just that the speaker drinks water in general (I drink water)
Because it is in present tense, there is no conjugation like English, so present tense always has the "r" on the end (other than in irregular verbs)
Actually that has a reason, something that has to do with the sound shift of the germanic languages. For more detail check grimm and verner laws..