Destroy the Super Mutants at the Watershed.

Destroy the super mutants at the Watershed is a side quest in Fallout.

Quick walkthrough

 * 1) Talk to Set peacefully and take the work he offers (optional).
 * 2) Kill the super mutants in the Watershed.
 * 3) Return to Set for your reward.

Detailed walkthrough
You need to start this quest before 110 game days have passed, or all the ghouls in Necropolis will have been killed by the super mutants of the Master. (If you have killed the Master before this time, the ghouls in Necropolis will be there forever.)

If you talk to Set, the leader of the Necropolis ghouls, and manage not to anger him, he will give you the opportunity to work for him. He wants you to kill the super mutants in the Watershed area. Alternatively, you can just go to the Watershed and kill all the super mutants first and then ask Set for payment afterward. Go to the Watershed through the sewers, and prepare for a difficult fight.

There are a total of six super mutants in the area, including Harry, who is the most heavily armed. Once all are dead, return to Set in the evening to receive your, frankly, paltry reward. If you then ask Set for the information you earned, he warns to tread lightly, as he could turn on you for it and you'd have to fight all of his ghouls.

Rewards
Normal:
 * 40 bottle caps
 * 4 Nuka-Cola
 * 4 flares

If Garret likes you:
 * 50 bottle caps
 * 1 shotgun
 * 40 12 gauge shotgun shell

If Garret really likes you:
 * 200 bottle caps
 * Less reward