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, making all mobs flow on to the side. It is impossible for either mobs or players to go 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 there.

The end of the water flow is blocked off in such a way the player can safely kill the mob by attacking its feet.