Thirst

Thirst is a mechanic similar to hunger. Over time, the thirst bar (seen above the hunger bar) depletes. To fill the thirst bar, you must drink water. Drinking water is done by holding shift and right-clicking water. However, unpurified water will give the thirst effect. If your thirst bar falls to zero, you will begin to die of dehydration. The thirst effect is essentially hunger for the thirst bar. During the duration of the effect, the thirst bar turns green as an indicator.

Purification
Water can be purified by cooking it in a furnace or blast furnace. This can be done with bottles of water and water bowls (purified water bowl texture is broken).

Canteen
The Canteen is an item which, when right-clicked on water, stores 3 drinks of water, equivalent to 3 bottles of water. The number of drinks left is shown in the tooltip. Canteens are very useful, and are crafted with 6 leather.