Following on BEARCAT’s Idea, to give the system a purpose, you can think of adding a REWARD PROGRAM. Personally, at this state of how the idea is presented, I don’t see any motivation to go all the way with an empty bottle to fill it up again (and paying for it?!?)…
…People are already doing this with tap water. Now if you probably want to go with the reward program, make sure it does not involve too many changes in the present infrastructure so that the project seems easily realizable.
You would need to review the ISSUE, the POSSIBLE SOLUTIONS, the CREDIBILITY and FEASIBILITY of those solutions and build on that. Do never stop at one Idea.