Sure, your XP number is your thirst. it starts at 20 and goes down to 0 where you will start dehydrating and taking damage (the same as starving). You drink from water bottles and can fill them up from any water source.
The number just above the xp bar is the thirst level. 20 being the highest, 1 being the lowest. If it gets below 1, you start to lose 1 heart per second. Fill up your water bottle at any water source. When you drink, your thirst should go back up to 20! You lose thirst at any time in game, walking or standing still.
