3e SRD:Holy Water
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Holy water damages undead and evil outsiders almost as if it were acid. Typically, a flask of holy water deals 2d4 points of damage to an undead creature or an evil outsider on a direct hit or 1 point of damage if it splashes such a creature. Also, holy water is considered blessed, which means it has special effects on certain creatures. A flask of holy water can be thrown as a grenadelike weapon. A flask breaks if thrown against the body of a corporeal creature, but against an incorporeal creature, the flask must be opened and the holy water poured out onto it. Thus, a character can only douse an incorporeal creature with holy water if he or she is adjacent to it. Doing so is a ranged touch attack that does not provoke attacks of opportunity.
Temples to good deities sell holy water at cost (making no profit) because they are happy to supply people with what they need to battle evil.