I wonder if this will come into use during any given apocalypse ....

• Blessing Water with Catholic Prayers and Ritual
  Gather and consecrate your salt.
  You will need to create holy salt before you can create holy water, so consecrate the salt (i.e. make it sacred or holy) first. Take some pure salt (e.g., Kosher salt or natural rock salt with no added ingredients) and add it to a container, such as a small bowl or jar. Once you are ready to bless the salt, say the following words from The Roman Ritual:[1]
  You can find the text of The Roman Ritual (or Rituale Romanum) online or purchase it as a book from a Catholic bookstore.
  There are no special requirements for the container you use for the salt. If you keep any holy salt that you do not mix with the water, make sure you mark the container so you don’t confuse it with regular table salt.
• Obtain some water from a natural source if possible.
  If you can, get your water from a nearby lake, stream, or river. Try to stay away from tap water, since it may have additives such as chlorine and fluoride in it. However, if your water is obtained naturally, filter it beforehand—you don't want dirty holy water!
  Place the water in an open container, such as a large bowl.
  You can also use tap water or bottled water if a natural source isn’t available. Store-bought distilled water or spring water are also good choices.
  Safety precaution: If you plan to sprinkle the holy water on yourself, put it on your lips, or drink it, it’s very important to make sure that it’s clean and well-filtered. You may get sick if you drink unclean holy water.[2]
  
• Exorcise the water.
  Before combining the salt and water, you will need to perform an exorcism over the water, as well. Recite these words from The Roman Ritual:[3]
  “O water, creature of God, I exorcise you in the name of God the Father almighty, and in the name of Jesus Christ His Son, our Lord, and in the power of the Holy Spirit. I exorcise you so that you may put to flight all the power of the Enemy, and be able to root out and supplant that Enemy with his apostate angels: through the power of our Lord Jesus Christ, Who will come to judge the living and the dead and the world by fire. Amen.”
  If you’re doing the exorcism in front of witnesses, have them join you in the following prayer: “O God, Who for the salvation of mankind has built Thy greatest mysteries on this substance, water, in Thy kindness hear our prayers and pour down the power of Thy blessing into this element, made ready for many kinds of purifications. May this, Thy creature, become an agent of divine grace in the service of Thy mysteries, to drive away evil spirits and dispel sickness, so that everything in the homes and other buildings of the faithful that is sprinkled with this water may be rid of all uncleanness and freed from every harm. Let no breath of infection, no disease-bearing air, remain in these places. May the wiles of the lurking Enemy prove of no avail. Let whatever might menace the safety and peace of those who live here be put to flight by the sprinkling of this water, so that the healthfulness, obtained by calling upon Thy holy name, may be made secure against all attack. Through our Lord Jesus Christ, Thy Son, Who lives and reigns with Thee in the unity of the Holy Spirit, God, for ever and ever. Amen.”
• Pour the salt into the water in the shape of a cross.
  Once you’ve exorcised both the salt and the water, the final step is to combine them. Add the salt to the water, making the form of a cross as you pour it in. As you pour in the salt, recite the following:
  “May this salt and water be mixed together; in the name of the Father, and of the Son, and of the Holy Spirit. Amen”
  If you are performing the ritual in front of witnesses, you should then say, “The Lord be with you.” They will respond, “May He also be with you.”
  Invite anyone present to join you in this prayer: “God, source of irresistible might and king of an invincible realm, the ever-glorious conqueror; who restrain the force of the adversary, silencing the uproar of his rage, and valiantly subduing his wickedness; in awe and humility we beg you, Lord, to regard with favor this creature thing of salt and water, to let the light of your kindness shine upon it, and to hallow it with the dew of your mercy; so that wherever it is sprinkled and your holy name is invoked, every assault of the unclean spirit may be baffled, and all dread of the serpent's venom be cast out. To us who entreat your mercy grant that the Holy Spirit may be with us wherever we may be; through Christ our Lord. Amen.”
• Bless the holy water.
  Once you’ve made your holy water, you can bless it using the following prayer from the Novus Ordo Book of Blessings: “Blessed are you, Lord, Almighty God, who deigned to bless us in Christ, the living water of our salvation, and to reform us interiorly, grant that we who are fortified by the sprinkling of or use of this water, the youth of the spirit being renewed by the power of the Holy Spirit, may walk always in newness of life.”[4]
  When you finish the blessing, make the sign of the cross over the water.
  You can find the text of this prayer from the Book of Blessings online or purchase the book from a Catholic bookstore.
• Use your holy water to bless your home and family.
  Once you’ve finished making your holy water, place it in the container of your choice, such as a small glass vial or plastic spray bottle. You can sprinkle it around different rooms in your home to bless them, or use it to bless yourself or a family member when they go to bed at night.[5]
  If you’re not comfortable using holy water that you blessed yourself, go to a priest in your parish and ask for some. Some churches also have a holy water fount where you can fill up a container to take home with you.

 

Creating Pagan Holy Water

• Collect sea water to use for cleansing and purification rituals.
  Sea water is already considered sacred in most Pagan traditions. If you’d like to use sea water for blessings and rituals, gather a little in a small bottle and leave an offering of thanks in return.[6]
  For example, you might leave some fresh flowers or a little food (such as fruit or vegetables) that the animals living in the area can eat.
• Gather rainwater for rituals of purity, fertility, and abundance.
  If you want to use water in fertility rituals, set out an open container, such as a glass jar or chalice, to gather some rain. You can also gather the water from a well or rainwater reservoir.[7]
  Water gathered during a lightning storm is thought to be infused with powerful energy.
  You can also collect morning dew for use in rituals relating to beauty, healing, and rejuvenation.
  Tip: Many Pagans believe you can use rainwater to help bring fertility to your garden. Simply use it to water your plants as you normally would. Don’t add salt if you plan to use it this way, though—it will damage your plants!
• Add salt to water for use in banishing spells.
  Practitioners of many religious traditions believe that salt can help ward off unfriendly spirits and entities. To make holy water for this purpose, place the water in a chalice. Say prayers over the salt and water that are appropriate for your particular Pagan tradition, then combine the 2 ingredients together and say a final prayer to bless the water and make it holy.[8]
  For example, you might first dip your fingers or a magic wand into the water and say the following prayer: “Behold this water that is the giver of life. I ask that this water be blessed and purified and made holy. In the name of Goddess and of God, in love, light, peace, and trust.”[9]
  Next, dip your fingers or wand into the salt and recite: “Behold the salt that is the preserver of life. I ask that this salt be blessed and consecrated and purified. In the name of Goddess and of God, in love, light, peace, and trust.”[10]
  Add a pinch of the salt to the water and mix them together, stirring in a clockwise direction. After you’re done mixing, say the final prayer while still touching the mixture of water and salt: “For, as the water is holy and as the salt is holy, may the union of these two be blessed and purified and consecrated. In the name of Goddess and of God, by the almighty power of Earth, Air, Fire, and Water, may this now be holy water, to be used in goodness, love, light, peace, and trust. So mote it be.”[11]
  Any kind of water or salt will work for this purpose, including tap water and table salt.
  In addition to dispelling negative energy, many Pagan magic practitioners believe you can use this type of holy water to bless and purify your body by gently dabbing it on your skin.
• Leave water outside in the moonlight for another way to make it holy.
  Many Pagans believe that simply exposing water to moonlight can make it holy. Put any type of water in the container of your choice and set it in a place where it will receive plenty of moonlight. You can “charge” this water with any intention you like and use it for a variety of purposes—for example, you might use it in love spells or purification rituals.[12]
  Preferably, you should use a silver or glass container for this purpose, since these materials are believed to be good at holding spiritual energy.
  As you set out the container of water, say a prayer or chant expressing your intention for the water. For example, you might ask for a blessing of love, purity, or protection. 
• Add silver to the water for additional lunar blessings.
  In addition to consecrating your water by moonlight, many Pagans believe you can bring extra lunar blessings by putting a piece of silver metal into the water. Choose any silver object, such as a ring or a coin, and drop it into the water before leaving it out in the moonlight.
  For a sunlight blessing, which is associated with healing and positive energy, you can add a piece of gold to the water and leave it out in the sun.
  Add silver to a bowl with snow and ice and charge it with an intention such as “freezing” your enemies or getting stuck energies to flow. You can then put this “Winter Blessing Water” out in the light of the full moon to make it holy.[13]