Holy water

Jamie McCrimmon, a Scottish Highlander from 1746, noted that witches were sprinkled with holy water. (TV: The Moonbase)

Holy water was also supposed to be dangerous to demons. During the 12th century, Henri d'Arrée dipped his sword in a font of holy water at a chapel to prepare for battle against the "forest demons"; when it had no more of an effect than a normal sword-blow, he deduced that the creatures were not demonic as he understood the word, despite being clearly "unnatural". (AUDIO: The Green Man)

Holy water could also dissolve vampires, although it was less effective against more powerful ones like S-Rank vampires. Vampires could detect attempts to trick them to their deaths by mixing holy water into blood, but not when unmitigated blood had been drawn from people who had drunk large quantities of holy water a short time prior, even though the latter kind was also still lethal to drinkers. Miss Garglespike attempted to exploit this in her plot to assassinate Zadok the Gory. One of the holy-water-drinking "donors", Venn, also found that, a short time after drinking holy water, his spit was lethally corrosive to vampires, melting one of Antrenor's eyes out of its socket when Venn spat in Antrenor's face in what he thought was merely empty defiance. (PROSE: The Bloodletters)