In my story, some people have the power of teleportation. I have constructed it in a way in which for teleportation to occur, it needs to be a water surface. All one needs to do is to see the reflection of the place they are attempting to reach in the water's surface and jump in. The water is acting as a sort of portal.
I want this to be an original thing, but knowing rules that have been used in the past would give me something to work with. I will construct my own limits for the sake of originality.
My question is, what guidelines can be put in place to restrict teleporters from simply teleporting anywhere without limit? I don't want them to require an item in order to teleport. They already need a water surface in order to teleport. Is there any other guidelines that has been used in the past to restrict teleportation that would make sense in this scenario? Original ideas would also be welcomed.
Thank you for the help.