Walter's Scrap Metal

 refers to an unmarked and repeatable quest in Fallout 3.

After the pipes in Megaton are fixed, Walter offers to buy Scrap Metal from you to maintain them.

Reward

 * Walter gives you 10 Bottle caps per Scrap Metal; if you decline payment, you will receive +10 Karma.
 * You also get a 5 XP reward per Scrap Metal you give Walter.

Bugs

 * If you bring Walter some Scrap Metal (tested with more than five Scrap Metal units) there is among the possible statements : "Eden wanted me to contaminate the water with a virus", which is something you can tell to Elder Owyn Lyons when coming back from Raven Rock. (confirmed on 360).
 * Walter, as most of Megaton's habitants is at risk of getting killed while wandering around the town by falling from the elevated passageways. Additionally, as the corpses of the subjects of such accidental deaths disappear after a certain time it is possible the corpse will not be there to be found, thus casting more confusion over the matter. Resurrection via console commands is available for players of the PC version, but for console players there's currently no fix.