A little grainy? It looks like it was filmed through Saran wrap.
The basic effect looks good, very clean. But I'm leery any time I see something done for just a web cam, it makes me think it won't work for the real world. How are the angles? What's the set up like? How difficult is the gimmick to acquire? Can the bottle be examined before and after?
Not a huge fan of the water drops splashing out when the coin goes in, it sort of telegraphs the method (As I presume it), and even if it doesn't, it would certainly lead the spectator to think that something fishy was going on, which is bad enough. Also, as ChristopherT asked, can the bottle be examined at all?
Well Before I go overboard and reveal anything, I am intending on releasing this as a free download for the wire.
But to answer some questions,
The Effect is angle proof
The Way I perform the routine I Start with a sealed bottle and drink from it casually so I haven't had any problems with anyone thinking something is fishy, although the bottle cannot be examined it is a powerful "on the fly" kind of thing and again I haven't been questioned.