Aqua Pura

 is literally "Pure Water" that is available once the add-on 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.