The Megaton purifier is the clean water source for Megaton.
Background[]
It is in the water processing plant and Walter fusses over it because it is always in need of repair. Left alone, it will break down. It requires scrap metal to keep going, which the Lone Wanderer can donate or sell to Walter to help him keep it running.
Related quests[]
Appearances[]
The Megaton purifier appears only in Fallout 3.