Throughout the Supernatural series, viewers will generally pay close attention to the weapons the Winchester Brothers make use of in their fight against demons, ghosts and the random vampire. In most cases, these weapons are normal, everyday household items and ones viewers recognize based from Christianity, but might not know the story behind those items.
In Anglicanism, Catholicism, Eastern Orthodoxy, Lutheranism, Oriental Orthodoxy, and some other churches, holy water is water which has been sanctified by a priest or bishop for the purpose of baptism, the blessing of persons, places, and objects; or as a means of "repelling evil"[i].
Number 301Catechism of the Catholic Church suggests holy water for protection from dark powers[ii].
Water has not had as much of an appearance in Supernatural as salt, however, it has had great importance in specific episodes. In these epsiodes, the water has been used as a way to defeat demons or to identify them. However, it does not work on the more powerful demons in the show[iii].
The use of Holy Water and its ineffectiveness was shown in the episode entitled Devil's Trap[iv]. In this episode, viewers are introduced to one of the first demons in the series. Up until now, he has only been known as "Yellow Eyes". He was the catalyst for the Winchester Boys' father becoming a hunter, after Yellow Eyes kills the Boys' mother. Yellow Eyes is a more power demon and is unaffected by the blessed water.
However, this is a rare instance. In the episodes Salvation and No Rest for the Wicked, the season finales for season one and three, respectively, Holy Water is used in rather original ways. In Salvation, John Winchester (Dean and Sam's father), actually goes on the roof of a warehouse and blesses the water in a tank. After a confrontation with a couple of demons, John runs to the water valve and opens it, turning the water on the demons[v].
In No Rest for the Wicked, the Boys have partnered up with another hunter named Bobby and in this episode, they are heading to a house to have a confrontation with the demon, Lilith. The entire town has been run over with demons. Bobby fills the house sprinkler system with Holy Water in order to give them some time to deal with Lilith[vi].
In the Sermon on the Mount, Jesus referred to his followers as the "salt of the earth".
The apostle Paul also encouraged Christians to "let your conversation be always full of grace, seasoned with salt" (Colossians 4:6) so that when others inquire about their beliefs, the Christian's answer generates a 'thirst' to know more about Christ. Salt may be added to the water "where it is customary" in the Roman Catholic rite of Holy water[vii].
Salt is usually associated with purification and protection and is used in this context in Supernatural.
In Supernatural, however, salt is not only a defensive mechanism to protect the Winchester Boys from demons and ghosts, it is also an offensive weapon. In almost every episode, salt is the weapon of choice. The Boys will usually lock, stock and barrel salt as weapons in their hunting rifles in order to shoot them at spirits. This will allow the Boys an opportunity to run away and find a good place to plan their next course of action[viii].
For the defensive, the Boys will make the traditional use of salt when it pertains to restless spirits. Sam and Dean will spread the salt around the window ledges, all the doors and along the edges of the floor. The purpose of this being that spirits and demons cannot cross over the salt, given its pure nature. Attempting to cross the barrier is usually futile, however, if even a smidgen of salt is remove from the barrier, it is rendered useless.
A good example of using salt is in the episode Devil's Trap[ix]. John Winchester is being held by demons in an apartment building. There is more than one demon present and demons are able to possess just about anyone. In order to minimize the opportunities, the Boys pull the fire alarm and once every tenant is out, they seal all the doors and windows with salt. This way, no more demons can get in, the Boys don't need to worry about innocent people and they're able to focus on rescuing their father.
The Rosary is a traditional Catholic devotion and is generally recognized through a set of prayer beads and devotional prayers. The prayers said at this time are usually related to the Blessed Virgin. The story of the Rosary is that it was gifted to St. Dominic by the Blessed Virgin Mary in 1214. Today, people who use the Rosary will usually recite the Lord's Prayer followed by ten recitations of the Hail Marys and a single recitation of Glory Be to the Father. Each of these sequences is meant to represent a decade. Following a decade, one is supposed to meditate on one of the Mysteries of the Rosary, which are events in the lives of Christ and his mother, the Blessed Virgin. Satan is also supposed to recoil from the prayers and the Rosary as he cannot handle their strength[x].
There are a few instances in the show where the Rosary is used, but the message definitely makes it through. In the episode Salvation, John Winchester uses the Rosary to bless the water in the tank that he later uses to fend off demons[xi]. In the season three episode, Jus in Bello, Dean uses the Rosary to bless the water in a toilet bowl in order to remove a demon from a human[xii]. In No Rest for the Wicked, Bobby uses the Rosary to bless the water in the sprinkler system to deter demons from entering a house[xiii].
[i] Holy Water – Wikipedia Entry
[iii] Holy Water in Supernatural – Supernatural FanWiki
[iv] Devil’s Trap Episode Recap – Supernatural FanWki
[v] Salvation Episode Recap – Supernatural FanWiki
[vi] No Rest for the Wicked Episode Recap – Supernatural FanWiki
[vii] Salt – Wikipedia Article
[viii] Salt in Supernatural – Supernatural FanWiki
[ix] Devil’s Trap Episode Recap – Supernatural FanWiki
[x] Rosary – Wikipedia Entry
[xi] Salvation Episode Recap – Supernatural FanWiki
[xii] Jus In
[xiii] No Rest for the Wicked Episode Recap – Supernatural FanWiki