This quest becomes available after Broken Steel has been downloaded and the quest Holy Water has been completed. In front of the town, where the normal caravans are, some Megaton settlers will try to take the Aqua Pura from the Brotherhood of Steel escorted scavenger.
Should the Lone Wanderer do nothing, the Brotherhood escorts will fight back and kill the settlers in the ensuing fight. Deputy Weld and Stockholm will likely be killed. The Brotherhood escorts will then say that the settlers attacked first, comment that the mission was all normal, and then continue on their way. If the settlers manage to defeat the Brotherhood entourage (an almost impossible outcome without outside intervention), each of them will take a bottle of Aqua Pura from the corpse of the brahmin caravan.
Passing a Speech check with one of the Brotherhood of Steel caravan guards will give the settlers the water, at the expense of Big Town's ration, thereby preventing the shootout. Alternatively, a Speech check can be used with the settlers to convince them to back off, preventing the shootout and allowing the caravan to be on its way.
- Good Karma
This quest may not be available if the Lone Wanderer does not visit the front of Megaton for several weeks after it becomes available.
If you convince the settlers to leave the caravan alone, wait until they walk through the Megaton gate, otherwise the next time you exit from Megaton they will be found fighting the water caravan. This happens if you went into town directly after solving the quest.