I am a big supporter of realism in a game like PZ, but not if it lessens the fun-factor for a majority of players. I think that this is one of those things. I hope that PZ implements a Hardcore or Realism mode that players can select. If that is the case, I think it would be great if they had this as an option...and since there is already a trait for Hard of Hearing, I do not think that this would be difficult to implement as a temporary condition when higher calibur weapons are fired by the player or very close to the player.
These bottles would be a nice little addition to office buildings and a good find when you do come across one, but I think game balance would be better if they were fairly uncommon as many could have already been taken by survivors. Also, they should not fit in a backpack. Instead, they could be implemented as their own carrying device that can only contain liquid. However, one question that may need to be decided is what happens when you add different liquids to the bottle such milk, water, alcohol, soda, etc...