File:Water floor.png

Summary
A typical water floor system converting a dungeon into a trap. The cobble/mossy cobble floor is dug out, and a line of water source blocks is put on the far wall. At the first dry blocks after the water flow ends naturally, a ditch is dug in with a single water source block at one end, making all mobs flow on to the other side. The ditch is deepened at the point the water ends to ensure it keeps flowing.

At the top right, a row of pistons is visible in the water as part of a system to block the water flows, for maintenance purposes. When raised, the actual line of water source blocks is contained behind it. Another such piston can be seen at the bottom, to block off the water flow in the ditch. When making such systems, care must be taken to make sure no light shines through, since pistons are technically transparent blocks. To get around this problem you can also use sticky pistons with a block on top, dug one layer deeper into the floor.

The end of the water flow is blocked off in such a way the player can safely kill the mob by attacking its feet, usually by only leaving the bottom half of the lowest block open by using half slabs.

Two hoppers are visible at the end of the stream to automatically collect drops from the killed mobs.