Dehydration

Dehydration or Thirst, sometimes displayed as H2O, is a derived statistic in Fallout: New Vegas in Hardcore mode.

Characteristics
Thirst increases over time, and can be affected by certain consumables. Much like radiation, it has increasing effects with each increment of 200. It primarily affects Endurance, though Perception, Intelligence, and Agility will also suffer with more severe thirst. A level of 1000 causes instant death. Without outside interference, it will take three days to reach fatal levels of thirst. It is the fastest-acting stat in Hardcore mode, accumulating twice as fast as food and about five times as fast as sleep.

Different foods and beverages have different levels of hydration. A drink from any faucet or body of water will confer a 200 point reduction per drink. Some beverages will decrease thirst. Liquor, soda and some foods will increase it instead.