@TiffanyMonroe Well, I have always loved folklore and myths since I was a child. I have a massive collection of books, some from even the 1800's discussing myths and lore from every country around the world. According to old myths about strigoi (what we now think of as vampires) and to a lesser extent, legends concerning demons or undead in other cultures as well, the undead cannot pass running water. (Think of the legend of Sleepy Hollow and the headless horseman, and how he could not cross the bridge).
In some times in history, bodies of the dead, suspected of being ghouls, vampires, and such, were actually weighed down and kept under water after death because it is believed that their natural element is "earth" and like mud, if the undead get in water, they can become trapped. This is also why it works in reverse, so like a Rusalka in folklore cannot leave the water.
Anyway! I try to do my best to weave real history and use actual folklore in my projects!