Aqua Cura is a counterfeit version of Aqua Pura, sold by Griffon and produced by switching out the pure water content with irradiated water to then sell to the ghouls in Underworld. He would then sell the real Aqua Cura to the people the Brotherhood of Steel wouldn't supply, such as the raiders and slavers, to further increase his profits.
Griffon also tries to increase his profits by marketing it to the ghouls as having effects that will benefit them. His claims includes that it cures ghoul skin problems in "just five minutes!"; cures clumsiness; helps sleep; removes stains; cures headaches; induces love; helps eyesight problems; promotes hair growth; helps concentration; improves hearing; prevents bullying; relieves "dry mouth, and other side effects of Mentats."; but best of all, it tastes great, and reverses radiation poisoning. Unfortunately its only real side effects to ghouls is restoring health, while furthering the "ghoulification" process.
Aqua Cura heals +10 hit points of health and adds a hefty dose of +6 rads when consumed. It is also more valued by traders than Aqua Pura, giving it a higher value when traded.
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.
Behind the scenes
Medicine shows as reflect in the game with Aqua Cura, selling "miracle cures" with Latin-sounding names and accompanied by a sense of showmanship, where common place during the Old West era in America.