Hey fellow piggie lovers! (I have a current herd of 24:1). Bit of a tip for you: I read this awhile ago, but can't find my way back to the source. But it seems true from what I have observed:
Guinea Pigs need to work their jaws in order to swallow properly. That is why your piggies want to chew their water bowl and bottle nozzle while drinking. Mine all do the same thing to bottles, and it takes them a loooong time to get the proper hang of a water dish (well, in our case, trough). The babies just chew the edge and get their noses wet, and the adults ... sort of shove their faces in it and chew/swallow.