I'm thinking of switching to nipple waterers, too - or at least have one handy because I go out of town occasionally. Here's what I might do: Have both types of waterers available for a while until they get skilled at getting to the water in the new one. Even then I might leave both out JIC. I won't switch to the nipple waterer without having the familiar one around though. With guineas...everything should go slow. They aren't bright, and they hate change.