One of my ex trainers used to ban drinking fluids in training. Even in summer (which can get pretty hot here) we were not allowed. He had a theory that it was bad for your kidneys or heart or something. I know a Chinese woman who thought that too because she was taught that in her high school track team (and she's in her late 20s) - it's dangerous not to drink when you're dehydrated. i don't know what ever made anyone think otherwise but these old beliefs still persist in some places!