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. It is impossible for either mobs or players to get from the ditch back onto the higher level. A door (bottom right) was added to allow the player to get out if he ever falls in the trap himself.

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. In this image, glass was added above the half-slabs.

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