Placing a bowl of water near the pillow will help prevent nightmares.

Jorge sleeps with a large bowl of water next to the head of his bed. He told me that it is something that he learned from his mother. Supposedly, the water will absorb any bad spirits or bad dreams, letting him sleep in peace. “It does help,” he told me. I asked him if this is a common custom in El Salvador, and he told me he is not sure. “You don’t really go around asking other people, you know,” he said.

This custom reveals the belief that bad dreams come from an external source, and can be captured physically. I find this belief to be an extremely common one—Native American dream-catchers purport to trap bad dream, the European succubus was definitely a physical creature—indeed the word nightmare echoes the widespread belief in the mara, the female creature who caused people to have nightmares by sitting upon their chests. Fortunately for Jorge, the source of his nightmares is soluble in water.

I think that this simple, convenient solution might also have inherited a belief in water as a powerful agent. Water is almost universally believed to have powers of purification—such as we see in so many religions. It seems like this folk remedy is an attempt to purify the air around the sleeper, cleansing it of whatever they are evil things that cause people to stir in their sleep.