I'm camped across the street from the dump station, so I see stuff.
Two days ago a couple in a C pull up and read the dump instructions. After a minute or so, they drive off and circle around to read the same instructions from the other side. Finally, I guess, they figured out what to do, so they drive around yet again and dump. While dumping, the man comes over to my site and asks me if that's "portable" water on either side. "Yes", I said, "that's what the sign says." He replied "well, my wife doesn't believe the signs." I said "well, don't believe me either!"
Today while dumping, I noticed there was what appeared to be one of the park's dump hoses on the potable water spigot. Sure enough, someone had taken the dump hose (with a clearly printed sleeve on it saying "not to be used for fresh water") and used it to fill their tank. And not replaced it.
I have a feeling I know who did that.