Man that's a classic hose water mistake. Did the same thing with my dog's bowl for months last summer. The water gets so hot sitting in that hose in the sun, it's basically cooking in there. My poor guy was drinking what felt like tea. Now I always run it for a minute to clear out the hot stuff first. Makes you feel pretty bad once you realize.
Forget the dog bowl, I made that mistake filling up a kiddie pool for my niece. She jumped right in and shot back out screaming. That water was scalding. It's one of those things you don't think about until it's too late. Running the hose first is just common sense, but it takes a bad experience to learn it.