"Christ in the Wilderness" by Ivan Kramskoy, Russian, 1872
Recently, I was questioned about the efficacy of holy water in an exorcism. The notion was met with disbelief. Perhaps it seemed like Catholic "superstition." So let's take a deeper look....
There is no water in hell. Water is a necessary source of life. In hell, there is only death. Perhaps this is why demons are said to dwell in the desert (Lv 16:10; Is 13:21; Is 34:14; Tb 8:3). It is arid, barren, and lifeless. It would be a familiar abode to hell's demons.
The New Testament witnesses to the waterless nature of hell. A pitiless rich man died and was committed to the "netherworld where he was in torment.... He cried out, 'Send Lazarus to dip the tip of his finger in water and cool my tongue, for I am suffering torment in these flames'" (Lk 16:23-24). He begged for a little water but, in hell, could have none.
At the beginning of his ministry, Jesus went into the desert, not just to be alone and pray, but also to confront and conquer Satan (Lk 4:1-13). Exorcizing Satan was, and remains, an essential part of Jesus' mission of ushering in the Kingdom.*
Likewise, the early monks in the 4th and 5th centuries went into the desert around Egypt, Palestine, and Syria to engage in spiritual warfare and conquer the devil, just as Jesus their model had done. The desert is a place of solitude; it is also an intensive abode of the demons.
Water is an essential element in baptism for the casting out Satan's influence and ushering in God's sanctifying grace. Similarly, holy water is used to cast out demons in the Rite of Exorcism. The new Rite of Exorcism appropriately reflects the baptismal rite.
Water is abhorrent to demons on the natural level. But when blessed by a priest, it becomes a source of grace on the supernatural level. The Church has the power and authority, given by Christ, to grace such sacramentals. These include blessed crucifixes, blessed salt and oil, blessed religious statues and many more.
One of the lessons I learned after doing years of exorcisms is how much the demons hate the Church and try to destroy it. And I often experience how powerful the Church is because of the living presence of Christ in it: "The gates of hell shall not prevail against it" (Mt 16:18).
A little water blessed by a priest doesn't seem like much. But when it touches demons, they scream in agony. When it touches the faithful, they receive God's blessing.
*See In the Name of Jesus: Exorcism among Early Christians by Graham H. Twelftree, Baker Academic, Grand Rapids, MI. 2007.