Water chip

The water purification control chip, usually called just the water chip is the cornerstone of the Vault-Tec Corporation's water purification systems installed in Vaults. The events of Fallout begin after Vault 13's only water chip breaks, and the only means to compensate for the diminishing water supplies is to leave and find a new chip.

Background
The chip that controls the system is a fine example of 21st century electronics. It is a large circuit board with embedded vacuum tubes that regulates the filtration systems inside the water purifier and monitors the output for signs of contamination. While the water chip can be jury-rigged for small scale water purification, it is specifically designed to interface with vault water computers (via a specific slot and jack; the chip still requires independent power supply through its own cord), making it useless for large scale water purification without a vault.

While it is theoretically designed to last, the chips were manufactured by a low-bid contractor, resulting in poor quality and a high failure rate. Such was the case with Vault 13 in 2161, made worse by the fact that the process was too complicated for a workaround system. However, they are easily replaced: Chips are interchangeable and work in any Vault water computer, they just require a self-test and reboot after connecting. The fact that they were shipped in boxes of five chips each is further testament to their expected failure rate.

Vault 13 did not have surplus water chips due to a clerical error. A shipping mishap resulted in Vault 8 receiving additional water chips that Vault 13 had ordered in place of their second allotted Garden of Eden Creation Kit. The GECK was instead shipped to Vault 13. 

Characteristics
The water chip is the MacGuffin that kickstarts the plot of Fallout and provides the impetus in the first act of the game. It has no additional role in the game beyond delivering it to Vault 13 to remove the initial time limit. In Fallout 2 it's a miscellaneous, largely worthless item found in bulk in the living quarters of Vault 8.

Locations

 * Vault 12's command center, in a computer.
 * One can be found in a locked footlocker in Vault 13.
 * A grand total of 420 chips can be found on the second floor of Vault 8, in crates in certain rooms that can only be opened with a high Lockpick or Strength.

Behind the scenes

 * The blueprint shown in the background of the intro is actually a schematic diagram for a Moog synthesizer.
 * In Fallout 2, the Guardian of Forever special encounter allows the player character to break the water chip and set the events of Fallout in motion.