The Watershed is a location in Necropolis inhabited by a group of super mutants. The area itself has a large water pump that provides water for the entire city, as well as two prison cells, and a tunnel that leads to Vault 12.
The Watershed was once inhabited by ghouls, though a group of super mutants led by Harry had taken over before the Vault Dweller visited. As a result, maintenance of the water pump became impossible, leading to it breaking. Instead, the city was forced to use the Vault 12 water chip for sustenance. If the Vault Dweller attempts to enter (or gets caught trying to sneak in) the watershed, Harry will stop them. Due to his lack of intelligence, he can easily be tricked into letting them pass, or else he will send them to Lou, his boss. Barry, Gary and Sally are the three super mutants along the hallway. Larry is the supposed guard outside and Terry protects the water rations.
The Watershed is composed of 5 buildings, from which the northern one is the most important, as the super mutants reside there. Inside the building, the mutant Harry stands guard, with some of his fellow mutants nearby. Also, in the eastern part is the water pump, the prison cells and even the entrance to Vault 12.
In the western building, some members of the Childen of the Cathedral reside there, who might aid the Vault Dweller for a small sum of money. The southern buildings are homes for some of the ghouls of Necropolis.
If Harry's team is killed and after 30 days the Dweller returns to Necropolis, three invasion mutants will be waiting outside the Watershed.
The Watershed appears only in the original Fallout.