Air is a limited resource that the player will slowly lose when they are underwater or in environments with no oxygen. Available air is measured through a UI element that appears when the player is losing breath. The breath meter decreases at a rate of 1 bar every 5 seconds when air is unavailable. Once it is empty the player will lose health and eventually die.
The air meter will refill itself when the player returns to a breathable environment at a rate of 2 bars per second.