Holy Water is Aqua Pura unknowingly stolen from Megaton by the Church of the Apostles of the Eternal Light (an offshoot of the Church of the Children of Atom) to which a large amount of "Atom's Light" (radiation) has been added in order to spread "the Glow of Atom's Light" to the "unenlightened."
While the Church of the Children of Atom wish for Division (getting their atoms split), the Apostles of the Eternal Light wish to feel Atom's Glow (become irradiated). They believe that becoming a ghoul is humanity's next step towards perfection, and so "bless" Aqua Pura to help people achieve this holy state.
- After Rosa gives holy water to Micky, she will give one bottle to the player. She has one more in her inventory. An additional one can be stolen from the beggar at this time, by picking his pocket after Rosa gives him the bottle but before he drinks it.
- On first meeting Brother Gerard he will hand the player a bottle. He has two to four more bottles in inventory, which can be pickpocketed.
- An infinite number can be obtained from Brother Gerard using an exploit. Drop all holy water and speak to him again, and he will hand over another bottle (this stops working after the first time the player drinks any, because that triggers the next step in Gerard's conversation script).
- Should the player have completed the quest Project Impurity by infecting the water supply with modified FEV Curie III would've irradiated the water effectively neutralizing the virus.
A message will report "holy water has worn off," similar to the message after drinking Aqua Pura. This may repeat at intervals indefinitely. There appears to be no ill effect. [verified]
- The Lone Wanderer: "How do you make your "holy water"?"
Curie III: "It was a gift from Atom. I was meditating right here in Springvale, when four of His armored angels came to me. When I said I was from Megaton, they gave me barrels of "Aqua Pura," and said I should share it with my people. They were very clear on that. But when I shared some with my Enlightened brethren, it made them terribly ill. I questioned why Atom had brought a pestilence upon us. That's when I thought to consecrate it with Atom's Light. And lo and behold, it removed the pestilence and made the finest holy water imaginable!"
(Curie III's dialogue) Note: This is the response given should the player have completed the quest Project Impurity by infecting the water supply with modified FEV.