I do not check this often, so this reply is "a bit late" However, this was designed for SMP, There are not many servers I have been on that do not give access to spawners. Also, from your initial comment, it looks like the redstone was broken when imported. The pistons in their default position are extended, holding back the water, then a mob spawns and hits the trip wire, which contracts the pistons, allowing the water to push mobs into the pit. When mobs are cleared, the whole thing basically resets for another round of mobs.
on July 4th, 2019 06:58 PM EST