(Why yes, now that you've asked, my last post does read rather harsh and callous now. But hindsight is always 20/20.)
It turns out that poor Mr. Snug was not ill from drinking toilet water. We don't know what really was wrong. But whatever it was, it was so wrong that he did not come home with me from the vet's this morning. Monday he was strange, yesterday he was downright ill. He was a suffering, dying cat this morning when I took him in. His body temperature was so low that the thermometer wouldn't give a reading--given the option to spend much time and money running tests, I chose to agree with nature that, in fact, Snug was all done being a kitty. Not a difficult decision, which surprised me. I just decided, and was at peace. Still, it's not nice to come home and realize he's not going to be sleeping in the tub any more, or eating my plants, or making water spots on the couch from licking it.
I miss my buddy.