Cauldron

A Cauldron is a block that can be filled with water when right-clicked upon with a Water Bucket. When filled, a Cauldron can be used to fill three Glass Bottles. These Water Bottles are key ingredients for the Brewing of Potions using a Brewing Stand. A Cauldron is currently, without the use of hacks or cheats the only way to get water into the Nether.

Trivia

 * Cauldrons cannot hold Lava or Milk, but the potions that were once put inside of it in Beta 1.9 Pre-Release 2 used the Lava texture.
 * When broken, Cauldrons that have water in it do not drop any water, only the Cauldron itself.
 * When a Cauldron is being mined with water in it, the water will start to get cracks in it as if it is a block.
 * As of 1.0.0, Cauldrons can be used to legitimately store water within the Nether, as opposed to water evaporating by trying to place it down with a bucket.
 * Even if a Cauldron has water in it, a Piston can push it.
 * Even if a Cauldron has water in it, it will not extinguish any living entities (mobs or players) that are on fire.
 * In creative mode, if you attempt to fly inside a cauldron with a block above your head, a glitch will occur causing you to be "stuck" in flight form without being able to lift or lower yourself.
 * Standing in a Cauldron while the cauldron is being pulled by a piston will cause you to go through the cauldron rather than to be carried with it.
 * On November 8, 2011, Jeb tweeted a reply to a suggestion for boiling food in a cauldron, saying he may consider it later.
 * It's possible to push a minecart inside of a cauldron by using pistons and slabs.
 * It is actually extremely inefficient to use cauldrons as a source to get water for potions since 1 source block of water is enough to produce an infinite number of water bottles, crafting a cauldron requires 4 more iron ingots than it takes to craft a bucket and a filled cauldron will only fill 3 bottles before it needs to be refilled itself. Thus, the cauldron's only actual purpose is for making potions in the Nether. They however are of some use if used in zones far away from water sources to collect rainwater (For example, in a Superflat world).
 * Fire goes out shortly after putting a Cauldron over it.
 * There is a glitch where if you use a Cauldron to fill an empty potion in the Nether, the potion won't appear in your inventory until you open a chest.
 * You cannot see most items dropped inside a Cauldron while it's filled with water.
 * You cannot sneak across a cauldron, as you can still fall in.
 * Arrows "stick" to the water in a cauldron.
 * A cauldron has approximately a 15.5% chance of being filled with at least one level of water when exposed to one session of rainfall (Tested with 1000 cauldrons during a regular 15 minute rainfall session).