This is a very late reply,,, but we use "ho" when using the pronoun "tum" - e.g. "Tum paani peethe ho." (You drink water.) "Tum" is used when we are referring to the second person in an informal context.
What do you drink (Present indefinite).... is different than ....what are you drinking. (Present continuous). In fact there are two more tenses in this category. What have you drunk (Present perfect) What have you been drinking (Present perfect continuous)
"What are you drinking?" is the only suitable translation. The other is a very unusual sentence which most likely would be wrong. You have to use the Present Continuous form in English in this instance.