Find the Water Thief

Find the Water Thief is a side quest in Fallout.

Detailed walkthrough
On January 5, 2162, the Vault Dweller is once again able to enter Vault 13. To receive this quest, he needs to speak to one of the following people in the vault:
 * Lyle located on the second level, second room from the left of the screen on the south side.
 * Cindy located on the second level, first room from the right of the screen on the south side.
 * The water guard located on level 3, outside the storeroom door.

After speaking to any of these people about the water thief, enter the room nearest the elevator on level three and stay there until midnight. A lone vault dweller will leave the elevator and walk around the level before entering the water storage room (the room with multiple lockers).

When he exits the room, the Vault Dweller needs to confront him and insist on searching him. This requires the Vault Dweller to pass a Charisma check, or he will attack. After he is searched, the Vault Dweller will be taken immediately to the Vault 13 officer, who will thank them for their aid, which completes the quest.

Rewards
The amount of experience varies based on how the Vault Dweller handled the situation:
 * 1000 XP for ending the matter peacefully.
 * 500 XP for killing the water thief.