"I was bringing water, they were drinking it!"
Translation:Eu aduceam apă, ei o beau!
No, because the lesson is trying to teach the imperfect tense (past action with indefinite time frame), which, in the case of a bea, is beau.
au băut (-o, drank IT) is past perfect (past action with definite closure), and falls outside the scope of the exercise.
Side-note, a bea present / imperfect forms:
Present: (eu) beau, (tu) bei, (el/ea) bea, (noi) bem, (voi) beți, (ei/ele) beau
Imperfect: (eu) beam, (tu) beai, (el/ea) bea, (noi) beam, (voi) beați, (ei/ele) beau