Effective Against
DemonHoly water is water that has been blessed by a priest or through a specific Latin ritual. It is one of the primary weapons against demons, acting as an acid-like substance that burns demonic flesh on contact. Hunters typically carry flasks, water guns, or even gallon jugs of holy water depending on the expected threat level.
Usage
Splashing holy water on a suspected demon is the fastest field test for demonic possession — the possessed person's skin will sizzle and burn, and the demon within will react with pain and rage. Larger quantities can be thrown as a weapon to create distance or disable a demon temporarily. Bobby Singer once rigged a ceiling-mounted sprinkler system loaded with holy water as a room-wide demon defense.
Holy water can be created by any ordained priest performing the blessing, or hunters can perform the blessing themselves using the Latin rite. The ritual requires standard water, salt, and the recitation of specific prayers.
Limitations
Holy water has no effect on angels, monsters, ghosts, or most other supernatural creatures — it is specifically an anti-demon tool. Higher-ranking demons are more resistant to it, experiencing pain but not being significantly incapacitated. Holy water does not exorcise a demon; it only causes pain and can be used to weaken a demon during an exorcism.
Real-World Basis
Holy water is a genuine element of Catholic and Orthodox Christian practice, used in blessings, baptisms, and the rite of exorcism. The Catholic Church's Roman Ritual includes specific prayers for blessing water, and holy water fonts are found at the entrance of Catholic churches worldwide. The use of holy water against demonic forces in the actual rite of exorcism directly inspires its use in Supernatural.