The Drowned's Dead Water

 is an epic catalyst which can be used in the process of upgrading Adaptive Augments related to the Metal Part II episode.

Obtained from

 * Metal Pt. II: The Phoenix Cannon
 * Metal Pt. II: Into the Dark Multiverse

Trivia

 * One piece of The Drowned's Dead Water is needed to breakthrough milestone rank 21 of an augment.