Find the Water Chip

Find the Water Chip is a main quest in Fallout.

Detailed walkthrough
Exit the cavern and travel towards Vault 15. Enter Shady Sands (there is a green circle denoting a location uncovered during the travel to Vault 15).

Shady Sands
A rope will be needed to enter the next location, Vault 15. This is the initial reason for travelling to Shady sands. Ropes can found, and stolen, from more than one place in the town but can be purchased, or again, stolen, from certain traders; many of these traders are located in the Hub. However, Seth at the entrance to Shady Sands is the most convenient.

After acquiring the rope, go to Vault 15.

Vault 15
The entrance to the vault is hidden in the uninhabited shack. Open the hatch and descend into the vault.

There are a few giant rats and mole rats in the area. Head towards the broken elevator and use the rope on the shaft to descend to the second level.

Scavenge the area for loot, including a Colt Rangemaster hunting rifle located on the second floor (2F), a H&K MP9 SMG (3F), a leather jacket (2F), a crowbar (3F) and another rope inside the locker on the second floor (2F). Use another rope on the second shaft and descend to the third level of the vault.

Proceed to where the command center should be. Once it is in sight, 500 XP is awarded for verifying that it is not salvageable. To acquire the XP and the message that states the chip is elsewhere, reach the bottom right corner of the facility.

The Hub
After coming out of Vault 15 empty handed, travel to the Hub. Ask Ian for directions.

Enter the large building labeled Water Merchants and speak to the Master Water Merchant, Martha Rastello.
 * If pressed about Necropolis she will reveal its location. Alternatively, Miss Stapleton sells a vault holodisk with the location of Necropolis.
 * She will also offer the option to send water to Vault 13 for varying prices. This will add another 100 days to the time limit, but reduced by the same amount for the mutant invasions (500 days normally in v1.0, 13 years in later versions).

Travel to Necropolis.

Necropolis
Use the manhole to enter the sewers and proceed north through the sewers to the Watershed area. If the Vault Dweller takes this route, they will come across a group of friendly ghoul refugees and they can get information on the Super Mutants from their leader. After this, keep heading north through the sewers and climb up the ladder at the end. Find a building to the north with some super mutants and an imprisoned ghoul. In order to navigate the area without combat, either convince the super mutant leader Harry with a high Speech skill, sneak past or confuse him by having extremely low Intelligence. Violence is an option, but if one fails to achieve a peaceful solution, Harry will either attack or send the player character to the Mariposa Military Base.

After dealing with the super mutants, free the ghoul prisoner. If he lives, he will identify the entrance to Vault 12 in the adjacent cell. However, the entrance can be opened without speaking to him.

Ghoul sentries inhabit the vault area and are hostile during night time. Travel to the third level using the elevator, and enter the command center area. Remove the water chip from the computer, which also grants +3 reputation. Doing this will turn the ghouls in the vault hostile.

After obtaining the chip, head back to Vault 13 and give the chip to Vault 13 Overseer.

After completing this quest, Vault 13 Overseer will give the quests to Destroy the source of the Mutants and Destroy the Mutant leader.

Rewards

 * 500 XP for finding the destroyed command center.
 * 7000 XP for giving the water chip to Vault 13 Overseer.

Related quests

 * Ask Water Merchant to help
 * Calm rebel faction
 * Find the Water Thief

Bugs

 * To keep the water chip, simply press the 0 key when the overseer asks for it. Afterward, the Vault Dweller will be at the computer, gain the 7500 XP, have the time limited removed, get the new quests from him and keep the chip. If the player character has a bag or backpack below the water chip in their inventory list, this will also keep the chip from disappearing.
 * There are two ways to "reset" the quest. The easiest is to talk to the water merchants. The other requires that the Vault Dweller kept the chip, returning to Necropolis and using it on the water computer, thereby also undoing the chip quest, which means the Vault Dweller can give the water chip to the overseer again for 7500 more XP. Using this cheat allows the Vault Dweller to keep the chip and then travel back and forth between the Hub and Vault 13, gaining 8500 XP each round trip and increasing the time limit all the while. This does not work on the fully patched Steam version.