If you place water to completely flood the floor area around a monster spawner, will it prevent monsters from spawning? Or can monsters still spawn in water? The wiki says:
It tries 4 times to place the mob at a random position in an 9 x 9 x 9 area, and gives up on placing that mob if it cannot find a valid position after the 4 attempts.
So is a block with water flowing over it valid? I'm asking both from the perspective of neutralizing a dungeon (making it safe) and from designing a dungeon trap (a floor with water flowing over it would direct mobs to the trap, but would it also prevent them from spawning in the first place).