"Piješ vodu?"

Translation: Do you drink water?

[popxrebellion]

Why does the word water become "vodu" instead of "voda"?

[VladaFu]

It is in the accusative case. Read the tips and notes (web only) or any other grammatical resource about grammatical cases.

[pma4w89A]

Would "Are you drinking water?" be fine, too?

[VladaFu]

yes