Cauldron

A Cauldron is a block that can hold water.

Obtaining
Cauldrons can be mined using any pickaxe. If mined without a pickaxe, it will drop nothing. When a cauldron is destroyed, any water inside it will be lost.

Crafting
A cauldron can be crafted from iron ingots.

Natural generation
A single empty cauldron is generated in each witch hut.

Usage
To fill a cauldron with water, right-click on the cauldron with a water bucket. A cauldron also has a chance to fill up with water when rained upon.

With water in it, a cauldron can be used to fill glass bottles (turning them into water bottles), wash dye off of leather armor or remove the top-most pattern layer of a banner. To use the cauldron, right-click on the cauldron with the glass bottle, leather armor or banner.

A cauldron will extinguish mobs on fire (including players) who fall into it. Each use (including extinguishing mobs) causes the water level in the cauldron to decrease by one-third. After it has been used three times, it will be empty and must be refilled before additional uses. Endermen in a filled cauldron don't take damage from the water in it.

A cauldron cannot be used to fill an empty bucket, and water bottles cannot be used to refill a cauldron. A cauldron can be filled from a water bucket in The Nether.

Redstone component
A cauldron can act as a power source for a redstone comparator. With a cauldron behind it (possibly separated by an unpowered solid block), a comparator will output a signal strength proportional to how full the cauldron is: 0 for empty, 1 for one-third full, 2 for two-thirds full, and 3 for completely full.

Video
Note: Many of the uses of cauldrons released since the video was made (from 1.3.1 onwards) are not stated in the video.

Trivia

 * Arrows "stick" to the water in a Cauldron.
 * If you try to sneak over a Cauldron, you can still fall in.
 * Inside a Cauldron is 0.313 blocks tall.
 * While a Cauldron that contains water is being broken, the water will show cracks as if it were a block.
 * A Cauldron can be placed in the nether and be filled with water using buckets, allowing players to brew in the Nether.