Water

"You might not consider water a "block" as such, because you can't pick it up and put it in your inventory without the help of a distinctly circular bucket, but we make the rules and we say it's a block. So there."

- Duncan Geere

Water is a natural fluid that generates abundantly in the Overworld.

Natural generation
Water naturally generates in the Overworld to form oceans, lakes, rivers and springs. It also generates in villages, desert wells, strongholds, woodland mansions, and ocean monuments. Water never generates in the Nether and instantly disappears or "evaporates" into steam if placed there with a bucket. However, water can be placed in the Nether in a cauldron.

In Bedrock Edition, water also generates as part of underwater ruins with loot chests, but only two water blocks generate: It is unknown whether this is intentional. This is not the case in the Java Edition; if an underwater ruin generates on the surface, no water generates. This also happens with shipwrecks.
 * One water block generates inside the loot chest, making it a waterlogged loot chest.
 * The other water block generates on top of the loot chest.

Technically, water generates below layer 63 by replacing air blocks that are not part of a cave or other structure, although underwater caves and underwater ravines become flooded with water.

Appearance
The textures in Bedrock Edition are somewhat different from those in Java Edition, shown here for comparison.

Obtaining
Water blocks do not exist as items, but water can be collected by using a bucket on a water source block or a full cauldron.

In Legacy Console and Bedrock Editions, it may be obtained as an item via inventory editing.

Swimming
The button for is the same as the button for jumping; non-swimming players and mobs sink slowly in water. Holding the swim button raises the player through the water, and when the surface is reached, the player bobs up and down. As of the 1.13 update controls were changed, however, now the run button can be used to put the player in "swim mode" when the player is completely submerged in water, and the mouse can then be used to direct movement. When in swim mode, the player is horizontal and one block high. The player has an arm-waving animation when viewed in third person or by other players. When not in swim mode, the jump and crouch buttons can be used to raise and lower the player through the water, significantly faster than in previous updates.

Swimming in water is considerably slower against currents (see Current below), but faster when going with the current.

Most mobs that can stand can also swim any time they are in water, except for iron golems and undead mobs. This can lead to drowning if the water is falling from above.

Water of any depth prevents any entity, including the player, from sustaining falling damage if they fall into it, regardless of the distance fallen.

Spreading
Water spreads horizontally and downwards into nearby air blocks. Water can spread downwards until it reaches the bottom of the world, and 7 blocks away horizontally from a source block on a flat surface. Water spreads at a rate of 1 block every 5 game ticks, or 4 blocks per second.

When spreading horizontally, a weight is assigned to every direction water can flow to. For each direction, this weight is initially set to 999. Then, for every adjacent block it can flow into, it tries to find a way down reachable in four or less blocks from the block it wants to flow to. When found, the flow weight for that direction is set to the shortest path distance to the way down. At last, water spreads to the directions with the lowest flow weight.

Spreading water extinguishes fire and washes away certain types of items or placed blocks, causing them to drop as items and then carrying them along in the flow until the edge of the spread. Affected items include plants (except trees), snow, torches, carpets, rails, redstone dust and some other redstone components, cobweb, end rods, mob heads, and flower pots.

Source blocks
A water source block is created from a flowing block that is horizontally next to 2 or more other source blocks, and sitting on top of a solid block or another water source block. This allows infinite water sources to exist, in which a new source block immediately forms in the space left by removing a source block with a bucket. Pools of still water can be created by placing water source blocks in a confined area.

A dispenser loaded with a filled bucket places a water source block in an empty block in front of it when activated. A dispenser loaded with an empty bucket and a water source right in front of it sucks the source into the bucket when activated.

In snowy biomes, water source blocks have a chance to turn into ice if directly under the sky. Ice blocks under brighter light levels melt back into water source blocks (except in the Nether). Ice reverts to water when broken.

Current
The current in a water block determines both the direction it appears to flow, and the direction an entity such as a player or boat is pushed from that block.

Water with a current pushes players and mobs at a speed of about 1.39 meters per second, or 25 blocks every 18 seconds.

The horizontal current in a water block is based on a vector sum of the flows to and from that block from its four horizontal neighbors. For example, if a block receives water from the north and sends it both south and east, but borders a solid block on its west edge, then a south-southeast current exits from that block, because 2 southward flows (in and out) are combined with 1 eastward flow (out). Thus, 16 horizontal directions are possible. If a branch in a channel is 2 blocks wide at its entrance, then entities float into it rather than continuing in a straight line.

Water blocks can cause a current downwards. A downward current in a water block is caused by the block below it. Most blocks that do not have a solid upper face cause downward current on above water blocks. Also ice and falling water blocks (blocks created by spreading downwards) cause downward current on the above water block. Falling water blocks have a downward current by default.

Light
In the Bedrock Edition, every block of water reduces light by 1 extra level (in addition to the normal fading-out of light). In Java Edition, water does not cause any additional decrease for block light, but diffuses sky light, causing the light to fade with depth. Underwater visibility changes depending on the biome the player is in. The Night Vision and Conduit Power effects increase underwater visibility.

Color
Water has several colors, depending on the biome.

Java Edition

 * Warm oceans biome have a light green color.
 * Lukewarm oceans and jungles have a  aquamarine color.
 * Regular oceans, most rivers, lakes, medium/lush (except jungles), neutral and other biomes have a blue color.
 * Cold oceans have a dark indigo color.
 * Frozen oceans and frozen rivers have a dark purple color.
 * Swamps have a light and dull green-gray color.
 * Other biomes not listed above have a blue color.

Water and lava
Water and lava can produce stone, cobblestone, or obsidian based on how they interact. If the water touches a lava source, the lava turns to obsidian. If both touch each other while flowing, cobblestone is made and no sources are removed, and if lava hits a water source, the water source turns to stone.

Damaging mobs
Water damages endermen, snow golems, and blazes, at a rate of per half second.

Slower mining speed
Players with their head underwater require 5 times the normal amount of time to mine blocks while standing on the ground, or 25 times while not on the ground. If a player wears a helmet with the Aqua Affinity enchantment, then underwater mining speed while standing on the ground is the same as on land, and 5 times slower if not standing on the ground.

Drowning
Players and mobs (except fish, turtles, dolphins, squid, guardians, elder guardians, undeads and iron golems) have a breath meter that lasts 15 seconds. After they run out of breath, they take drowning damage every second until they die or surface.

Dolphins are a special case in drowning: they take drowning damage when underwater for about 4 minutes, but also take suffocation damage when in air for about 2 minutes.

Each level of the Respiration enchantment adds 15 seconds to the breath meter and grant an x/(x+1) chance (where x is the Respiration level) of not taking damage after that time: 30 seconds and an average /second with Respiration I, 45 seconds and an average of $2/3$ damage/second with Respiration II, and 60 seconds and an average of $1/2$ damage/second with Respiration III.

If a husk drowns underwater, it starts to shake and eventually becomes a zombie. If a zombie drowns underwater, it starts to shake and eventually transforms into a drowned.

Hardening concrete powder
When water comes into contact with concrete powder, the powder hardens into solid concrete.

Sponges
When a dry sponge comes into contact with a water source or flowing block, it becomes a wet sponge, absorbing all of the water within 3 to 5 blocks in all directions. Kelp and lily pads within the absorbed water blocks are destroyed and drop as items, and seagrass is destroyed without dropping anything. Mobs that take damage out of water are affected as a side-effect.

Sponges do not absorb water from waterlogged blocks, nor water that comes into contact by flowing back in from outside the area of absorption. For instance, placing a sponge 4 or more blocks from a single water source removes the flowing water in the area of effect, but as the flow from the source resumes it is not affected by the wet sponge.

A sponge instantly absorbs nearby water when it is placed next to water or when water comes into contact with it (by being placed next to the sponge, or by flowing towards it). A sponge absorbs water around itself (water source blocks or flowing water) out to a taxicab distance of 7 in all directions (including up and down), but won't absorb more than 65 blocks of water (water closest to the sponge is absorbed first). The absorption propagates only from water to water and does not "jump over" non-water blocks (including air).

Dripping
Water above a non-transparent block (does not include stairs, fences, and slabs) produces dripping particles on the underside of that block. These droplets are purely aesthetic.

ID
Java Edition:

Bedrock Edition:

Water spends most of its time as stationary, rather than 'flowing' – regardless of its level, or whether it contains a current downwards or to the side. When specifically triggered by a block update, water changes to 'flowing', updates its level, then changes back to stationary. Water springs are generated as flowing, and oceans, lakes, and rivers are generated as stationary. This happens before most types of generated structure are created, and the main cause of water "glitches" is that generated structures do not trigger a block update to let water flow into them.

Block data
If bit 0x8 is set, this liquid is "falling" and spreads only downward. At this level, the lower bits are essentially ignored, because this block is then at its highest fluid level.

The lower three bits are the fluid block's level. 0x0 is the highest fluid level (not necessarily filling the block - this depends on the neighboring fluid blocks above each upper corner of the block). Data values increase as the fluid level of the block drops: 0x1 is next highest, 0x2 lower, on through 0x7, the lowest fluid level. Along a line on a flat plane, water drops one level per meter from the source.

Trivia

 * While underwater, the player's FOV (field of vision) is lowered by 10 to simulate light refraction.
 * The old water texture can still be found in the assets and is used in the game if the player is underwater.
 * Water does not prevent explosions from activating. This effect is due to water's very high blast resistance, causing it to absorb any normal blasts, with the exception of explosions from Underwater TNT.
 * If a player with the levitation debuff is touching water, the effects of levitation are completely negated.
 * Water has collision detection even if the coordinates exceed 8,388,608 blocks. Water can therefore be used to travel to the Far Lands without falling through the world..
 * A glitch $2/3$ allows a water block to appear in the player's inventory.