It is produced by the ghoul Griffon by switching aqua pura with irradiated water to sell to the ghouls in Underworld. He would then sell the real aqua pura to people the Brotherhood of Steel won't give it to, such as the raiders and slavers, to increase his profits. It is essentially dirty water.
Griffon also tries to increase his profits on the water by telling the ghouls it has effects that will benefit them (which it does, because radiation heals ghouls, but it also furthers their "ghoulification".)
Several are found in boxes on/right of the table next to Griffon.
It can be bought from Griffon (which costs 10 caps)
If a certain speech challenge is used to complete the quest The Amazing Aqua Cura!, Griffon will then sell regular aqua pura, although he will continue to call it aqua cura, which he claims is to give hope to the ghouls that purchase the water (though it is probably for marketing reasons). Stealing a bottle of aqua cura after completing the quest in this way will reveal that it is still heavily irradiated, though this may be old stock or simply for display.
Griffon claims that aqua cura:
Cures ghoul skin problems in "Just five minutes!"
Helps eyesight problems.
Helps hair growth.
Tastes great, and reverses radiation poisoning.
Relieves "dry mouth, and other side effects of Mentats."
Aqua cura is worth more than aqua pura with all traders.
Aqua cura appears to lose its radiation level over time in your items while accomplishing other quests, etc. Effect becomes: Rads +0 but still gives Rads +1 when consumed. No known amount of time when this occurs has been agreed on but somewhere between 2–7 days by the game clock should provide this result.
Griffon can only sell you up to two bottles of aqua cura.
The water in the bottle, when viewed closely, and under certain lighting effects,has a slight red appearance. Possibly blood from Griffon's enemies' corpses, a situation not unlike the plot of Soylent Green.
Behind the scenes
Selling quack cures with Latin-sounding names and accompanied by a sense of showmanship is an American tradition.