Help with a detail in my book? Thanks a lot! :)?

I'm writing a sequal to my demigod book, and I have a question about the Underworld in Greek Mythology. I tried looking a bunch of other places, but none had the specific answer I was looking for. Anywho, this is my question: I know from "The Theft of Persphone" that you can't eat anything in the Underworld, but can you drink anything. In my book, the character is confused on where he is, and he drinks some water from this river-type thing. Later on, I realized that he wouldn't be able to leave the Underworld, and i even made it a point of mentioning how you can't eat anything there. By eat, do they mean like any type of 'sustenance' including water, or just solid food? Thanks for any help! :)