Minecraft Fluid

Fluid

Liquids (fluids) are special blocks that flow freely, forming rivers, waterfalls, and lakes.

Overview

Two liquids: water and lava. All liquid blocks originate from source blocks (full blocks). Confined sources (surrounded by solid or liquid blocks) don't flow and render still; once at least part is unconfined, they flow per basic fluid dynamics, rendering flowing with animated directional lines; flowing blocks get shallower with distance.

Liquids interact with each other and with blocks; they push most entities/items (drown or float). Most mobs (including players) can swim/float; undead generally can't swim well. Sources can be picked up with buckets (Java: liquids have no item form). Liquid blocks are replaceable — placing a block replaces them. Java: snow doesn't accumulate under liquids; water under water doesn't freeze.

Mechanics

Depth

Depth describes how "empty" a block is: sources are always depth 0; horizontal flow increases depth by 1 per block from the source; max depth 7 (no more horizontal spreading beyond). Vertically falling liquid is depth 0. Lava's max depth is 3 in the Overworld/End, but 7 in the Nether.

Spreading

When a source is placed (in air or waterlogging), it's added to a spreading queue. It first tries to form streams on each open face — a flat surface spreads in four directions up to the depth limit (a floating source still spreads 1 block horizontally even with air below). Then, for the block below the source and each flowing block in the queue:

1. Air → replaced by liquid.
2. Waterlogged non-solid block → stop (each waterlogged block has its own queue).
3. Fluid-affected non-solid blocks, bamboo shoots, cobwebs → try to drop as items and get replaced; the upper block is removed from the queue.
4. Solid blocks (or a few unaffected non-solids) → spread to the four open faces; new flows join the queue.
5. Another liquid → liquid mixing; new flows join the queue.
6. Same-liquid source → stop.
7. All four neighbors solid → stop (why 1-block-wide columns don't spread at the ground).

At max depth no horizontal spreading happens. Flow speed: water 1 block per 5 ticks (0.25 s; can't be placed in the Nether but still flows); lava 1 block per 60 ticks (3 s) in the Overworld/End, 1 per 10 ticks (0.5 s) in the Nether.

Flow Direction

The liquid checks terrain within 5 blocks/horizontal flow distance for air, pure liquid, or flushable blocks below (Java: also waterlogged blocks with exposed liquid tops) and tries to form streams toward the nearest found spot (1-block-wide streams near edges; those blocks are removed from the spreading queue).

Java water source conversion: with the water_source_conversion game rule true, a non-waterlogged waterloggable block horizontally adjacent to ≥2 water source blocks (or waterlogged blocks with unobstructed liquid faces; flowing water counts as full) with a solid/water/waterlogged block below becomes waterlogged when water flows into it.

Droplets

With particles fully enabled, dripping particles form under blocks with liquid above (Java: blocks whose top touches liquid and whose bottom is above the neighbor below). Lava droplets don't damage or ignite. Newly placed liquid takes seconds to "percolate" before dripping.

Block Updates (Java)

Liquid updates from NC updates (liquid flowing in / neighbor drying) and PP updates (depth changes). Structure generation never updates liquids on load — e.g. cave entrances cut into underground lakes stay static until something updates them; structure-generated liquids flow immediately.

Liquid Interactions

Two behaviors: touch (adjacent blocks) and flow-in (occupying the same block). Flow-in requires touch first. Results (all reactions happen on the lava side):

• Lava source touching water horizontally or above → obsidian.
• Lava source/flow touching water below → no reaction.
• Lava flow touching water horizontally or above → cobblestone.
• Lava flowing down into water → stone.
• Lava touching soul soil below + blue ice horizontally/above → basalt.

Notes: down-flowing tendencies make the "no reaction" cases transient; the only permanent no-reaction case is lava above a waterlogged block (blocks the flow). Horizontal lava-water contact only touches (reacts immediately); vertically only lava flows into water (water touching lava reacts); all reactions occur on the lava side.