Fluid

There are currently only two fluids in Minecraft, Lava and Water.

How Fluids Work
Fluids are cellular automata. The rules appear to be as follows.

Falling fluid
An air block below a fluid block is converted into a fluid block of that type. This happens faster for water than for lava.

Fluid Level
Each fluid block has a level value. Source blocks have a level of 0, and the maximum level depends on fluid type.


 * Water 7
 * Lava 3

Note: The "Level" value increases as the water is further from the source. A high Level value means that the water is actually physically downhill.

Still Fluids
To keep track of which blocks are actively flowing, Water and Lava each have a pair of block IDs. For water, there is Water(8) and Still Water(9). Still Water never updates. Water updates periodically and will change itself to Still Water when it cannot spread any further.

Changing a block next to Still Water will turn it back to Water so it can spread some more.

If you edit either type of fluid block into your inventory, they will spread when placed, since placing a block causes updates.

Fluid Block Update Times
The state of a fluid block only updates at certain times


 * on creation
 * if one of the 6 neighbouring block's state changes.
 * if its own level changes

State changes that cause an update include
 * Adding or removing a block
 * A neighbouring block's level changes
 * A redstone wire switches on or off

Fluid Block Update Process
When a fluid block updates, it performs the following checks.


 * Check inward flow
 * If there is a fluid block of the same type above, set level to 1
 * Otherwise, reduce or increase level in steps of 1 so that it is 1 higher than the one of its 4 neighbouring block with the lowest level*
 * If level is increased past the max level, replace fluid block with air block.
 * Level cannot be decreased below 1

* This does not affect source blocks (level=0)


 * Check outward flow
 * This only happen for fluid blocks of less than the max level value
 * Determine the shortest distance to a fall, but only scan 8 blocks distance*
 * If any of the directions tied for shortest have an air block, convert that air block to a fluid block with a level of 1 more than the current block)*

* This means that lava will flow towards a drop that it cannot reach.

Source creation (water only)
A water block is converted into a source block if all three of these conditions hold:
 * it is bordered by 2 water sources
 * the 2 sources are on the same horizontal level as it
 * there is a solid, opaque block underneath it

Mixing of fluids
Mixing of fluids cause cobblestone to be produced, except that if water flows into a lava source block, then obsidian is produced.

When determining the shortest distance to a drop, other fluid blocks are assumed to be equal to air.