Aqua Pura

 is literally "Pure Water" that is available once the DLC pack Broken Steel is installed.

Drinking the water after choosing to infect it with the Modified FEV will result in a player debuff (-2 STR and -1 INT) and, if you drink too many, you will die (this is usually any more than two, so be careful.

Bugs

 * Giving any amount of Aqua Pura to Water Beggars will result in their death at the next map change, regardless of whether or not the Aqua Pura contains Modified FEV.
 * Sometimes the message 'Aqua Pura has worn off' will appear, even if you drink non-FEV water. This is likely due to both the FEV and non-FEV effects being on the same bottle and the application of either controlled by quest flag conditions: The FEV-infected Aqua Pura spell duration is applied, but the effects are nullified because conditions are failed.
 * Possible bug: If you didn't give the FEV bottle to Elder Lyons, even if you don't insert it into the purifier the Aqua Pura still gets corrupted.