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 applied into water purification system.

According to President Eden it will wipe out super mutants, Ghouls and unclean citizens. The only people who will survive are pure strain humans.

In the DLC Broken Steel, if the player had chosen to contaminate the purifier with the Modified FEV, the medical facility of every city is filled with new patients dying from FEV poisoning. 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 comments along the lines of, "it would be ironic if we were so used to the crap we had been drinking that pure water is killing us."

Related quests

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