Another correct, albeit a bit old fashioned, answer would be: ze waren dorstig dus dronken water
I thought the word order after the comma has to be flipped (i.e. zo dronken water ze").
I was wondering the same... Why not "dus dronken ze water"?
For "dus", both "dus dronken ze water" and "dus ze dronken water" work. In the first sentence, "dus" is an adverb. In the second sentence, "dus" is a coordinating conjunction. Both possibilities are correct and there is no difference in meaning.
Why not: ... dus ze water dronken?