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 drinks have different levels of hydration. A drink from any faucet will confer a 200 point reduction per drink. Most beverages will decrease thirst to some extent; most types of liquor, however, will increase it instead. Some types of food may increase or decrease it, as well, though usually not to any significant extent. For example, Nuka-Cola, Sunset Sarsaparilla, and Pork n' beans are three consumables which negatively affect thirst.