Plain water? And it didn't leak?
But if you just want to use plain water, isn't it easier to just throw your coil heads in a glass bowl, cover with distilled water and nuke them for a few minutes? That's what I tried in the past, but never got very satisfying results. Water alone won't dissolve the coil gunk. It will clean the filler a little, but not the coil.
PG/VG and vodka are better solvents, in my experience.