Modified FEV

 is a modified strain of the Forced Evolutionary Virus developed by John Henry Eden, based on the earlier FEV Curling-13 strain used by the Enclave in 2241, only now it was designed to be placed into a water purification system, it is received after dialogue with President John Henry Eden.

According to President Eden it will wipe out super mutants, ghouls, and all other "unclean" citizens, namely anyone who had been born in the Wastelands and exposed to their radiation and other mutational effects from birth. The only people who would survive the infection are pure strain humans and humans who were born in the Vaults. Of course, it should be noted that by this point in the plot it has been established that the Lone Wanderer wasn't actually born in Vault 101 as he was raised to believe.

In the add-on Broken Steel, if the player had chosen to contaminate the Purifier with the Modified FEV, the medical facility of every city in the Capital Wasteland (except Tenpenny Tower) is filled with new patients dying from FEV infection. The new patients hold their stomachs and repeat dialogue along the lines of, "it burns on the inside." When the player speaks with the doctor at any given town, they state that the condition is not contagious. In Rivet City, Dr. Preston comments that they are burning the corpses just to be safe. In Megaton, Doc Church makes a comment along the lines of, "it'd be damned ironic if we were so used to the crap we had been drinking that actual pure water was killing us." If the Lone Wanderer drinks three bottles of Aqua Pura, he/she will die.

Related quests

 * The American Dream
 * Project Impurity
 * Take it Back!