Water

Water is a liquid that can put out Fire and Lava. It has different Game Mechanics than Lava - It flows faster and does not make the player take damage directly, although players can drown in water. Water spawns naturally in the form of lakes, oceans, waterfalls, and rivers.

Infinite Water Source
Water is a renewable resource, meaning that it can be renewed infinitely. Arranging water source blocks in a 4x4 square creates an infinite water source.

Danger
In Large bodies of water, players can drown if they stay underwater for too long, which might occur if swimming over large stretches of water. Also, Animals caught in a waterfall may drown.

Trivia

 * Water can be put in buckets similar to milk and lava.
 * Endermen take damage from coming in contact with water.
 * Water dripping particles were added in the 0.9.0 update.
 * It can also be found in the form of a fountain in strongholds.
 * Infinite Water Sources can be found inside Village Wells.
 * Squids are only mobs that don't drown in water.
 * If a sugar cane is planted around water on the same level, it will it destroy the sugar cane.
 * This is useful in making permanent air pockets when diving into deep ocean biomes.