In Christianity. In Catholicism, Lutheranism, Anglicanism, Eastern Orthodoxy, Oriental Orthodoxy and some other churches, holy water is water that has been sanctified by a priest for the purpose of baptism, for the blessing of persons, places, and objects, or as a means of repelling evil.
It can banish demons, heal the sick, and send unwarranted grace upon us—yet most of the time we cross ourselves with this water without even thinking about how holy it really is. The fact of the matter is that holy water is a powerful sacramental and we ought to use it daily.