Dehydration

H2O, or Thirst, is a derived statistic in Fallout: New Vegas in Hardcore Mode.

Characteristics
Thirst is affected by certain consumables and other things. Your endurance will decrease as you become dehydrated, which get worse over time. If you do not drink a suitable drink in 3 days, you will die.

Stages of Dehydration
Minor Dehydration(200-399): Endurance -1.

Advanced Dehydration(400-599): Perception -1, Endurance -2.

Critical Dehydration(600-799): Intelligence -1, Perception -2, Endurance -3.

Deadly Dehydration(800-999): Intelligence -1, Perception -2, Agility -2, Endurance -3.