I am running a server that has Thaumcraft and Mr Crayfish's Furniture Mod as the two core mods. Recently players have been complaining of FPS issues near some housing they have built.

I tracked the issue down to the mcf showerheads that had been placed in each of the 4 buildings. Just 4 showerheads reduced my fps from 60 to ~11

In testing to find this issue, I found that a single showerhead would reduce my FPS from 60 to 40, until I turned it on, the FPS while it is operating is normal, but turning it off brings back the FPS penalty.