How come water signs makes such horrible teachers?

It's all in the names of the signs: Water signs are good at changing which is nice in a personal relationship but not something you can depend on, especially when this person is teaching. Fire signs are dedicated and pionate, so if they set their mind to something like communicating some information, they can do it convincingly. Earth signs are known for being steady and determined, and they know their way with matters of the Earth, the world around them, and the people in it. They are rational thinkers so they stick to fact.