Wells are believed to be passageways for ghosts and spirits to enter the physical world.
If a home or building is on top of a well, then it will be haunted. Covering the well is believed to exacerbate the haunting, for it will frustrate spirits seeking access to the physical world.
They will clamor about looking for another access route. Wells – and water in general – have a long history of supernatural beliefs.
Lakes and rivers are the dwelling places of a host of water entities, gods and goddesses, monsters, dwarfs, undines (a type of fairy living in or by bodies of water, and other creatures, some of whom are guardians of the water as well.
Longstanding customs exist for propitiating the spirits with offerings tossed into the waters.
Wishing wells and even cursing wells derive from these beliefs.
Water is believed to have spiritually purifying properties: evil things cannot cross running water.
Many wells and springs are ascribed healing properties and are turned into holy shrines.
Various wells also are known for their divinatory properties: one sees the future in the water. : Airbender.