This has happened with plain water for me. I used to drink a lot of water before surgery, but since day 1 after surgery every single sip of water makes me violently sick. After 1 day, they switched water with apple juice, and I was fine. I'm 15 days post-op now, and I still cannot tolerate plain water. I dilute apple juice with water and it's fine as long as it has some flavour in it.