Minecraft wiki entry for Things_not_to_do, associated text: Extinguish fire
Solidify pools of lava to a walkable surface of obsidian
Safely descend cliffs
Allow the user to scale cliffs
Repel endermen without aggravating them
Kill melee mobs easily, as they are slower in water
Be placed on the ground to break a fall
Be placed on the ground, then used with a fishing rod, to generate a mobile food source