40 years ago, in the alternate past of the year 2020, a killer disease spread through the entire world due to its waterborne nature which poisoned all people who drank it. Over time, clean, uncontaminated water became the most valuable resource to the very few who remain. The main character who was an engineer, (who does not have a name) has a very rare machine known as a water decontaminator. Unfortunately, one day it breaks leaving him with exactly 3 days' worth of clean water. To avoid his eventual demise, the character plots a course to wander across the wasteland to an old-world lab in search of a component that can fix his own purifier. However, during his adventure, he encounters others who wish to kill him and steal his water. Despite this he presses forward and begins to learn how the world outside his bunker works.