Nothing but bottled water is a perfectly acceptable rule. In fact, that is the rule for our whole sanctuary and that is pretty common. If people are responsible you can let other bottled beverages with a cap slide, but it all depends their level of responsibility (I generally have some caffeine handy myself). I have always had a bottled water only rule in place and simply threw away any open drinks that were in or on the sound booth (one that turned out to belong to a Pastor's wife, but the Pastor defended my actions). Most volunteers couldn't pay for a console if they broke it anyway, so simply saying that they would have to doesn't usually do much good in my experience.
If you approach the rule as a way to be a good steward of God's property than anyone who has an issue with the rule or with you may not be the best servant for the job anyway imho.