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).
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.
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?
Is feminine nominative plural generally the same as geneitive singular? e.g. kanapki, sukienki, wody
Yes, for feminine nouns, the following are usually the same: Genitive singular, Nominative plural, Accusative plural. Not always, but usually.