Second opinion] is it considered theft to take bottled water…

CCTV footage may be evidence against you, but they would still have to establish that you should have known you were not entitled to take the drink, which from your own evidence is far from clear.
In any event, if they haven't used such evidence after a month then it is hard to see them raising the issue now. After all, it was only over a bottle of water. Likely it isn't worth the police time to even check the video, and in practice CCTV footage involves hours of tape and is not viewed unless something unless someone is actually looking for evidence of something. So if they actually know or believe you stole the drink and are out to 'get you' then they might look at the footage to find evidence to prove you stole the drink bottle, but if that were the case I would have expected it to happen by now.

If no one is raising a stink about it already then I think you are quite safe.

The worst likely scenario is that you are convicted of larceny, incur a criminal record and are ordered to pay a fine, do community service and/or have a good behavior bond. Whilst a brief term of imprisonment is theoretically likely unless you have a long criminal history, such a penalty is implausible. Frankly though, I think you have little to worry about at this point.

Good luck and please rate my answer.

Patrick

Within a week or so of the police investigating the matter and concluding they have sufficient evidence to proceed.

The limitation period for summary offences in Victoria, such as this one, is 1 year:
http://www.austlii.edu.au/au/legis/vic/consol_act/cpa2009188/s7.html

No idea. These are the sorts of issues they will struggle with which mean they will likely find it just too hard to do over a bottle of water.