I read an old short-story about a girl (the title of the story/book was ''Just One Cup of Water could Kill Little Heidi'') who would go into anaphylaxis if she got even a teeny drop of water in her mouth (requiring adrenaline shots to save her life) as her immune system saw H2O molecules as foreign and she was born this way. For example early on in the story she accidentally drank a mouthful of water and almost died.
The story said she once had surgery and was given a drip afterwards, and went into shock because the drip was ''water based'' and she was getting water injected into her veins.
She had to wear a spacesuit like contraption to avoid breathing in the water vapor (H2O molecules) in the air as that could instantly kill her since her immune system saw H2O molecules as foreign if she got any of them inside of her body.
So I Googled ''IgE antibodies against H2O'' or ''anaphylaxis to the H2O molecule being ingested'' and couldn't find anything. Closest thing I could find was skin irritation (called Aquagenic Urticaria), but not an allergy, upon contact with water. Anaphylaxis isn't a symptom of it though and doesn't match the girl's condition in the story.
This story is very popular in my country and several news websites have ran sequels and variations of it, while reporting it as if it were a genuine news story.