How dare you not being hydrated >:(
Why is it wody and not wodę ??
Because of the 'nie'. Negated verbs usually take genitive (wody) instead of accusative (wodę).
Can't we say "he drinks no water"? If I translate this sentence to polish using google translate, it gives me "Nie pije wody". Is this correct? If it is, then isn't my translation equivalent to the given one?
It's because "nie" comes before "pije" so it negates "drinking", changing it to "not drinking." To negate water, just like in English with the word "no", "nie" must come before "wody."
I don't think you can say On pije nie wody.
But I reckon one can say "On pije nie wodę." (He is drinking not water but something else).
Well, in theory... it's hard for me to imagine someone actually saying this. And I wonder if it wouldn't be spelled as "niewodę". Generally safer to say that it's just wrong.
How would you say, "He does not drink water"?
The same. For 99% of the verbs, Polish does not show a difference between English Present Simple and Present Continuous.