Is there a rule for when you can shorten the word "nu"? Like in "Caii n-au apă." If I had to take a wild guess, I'd say only when the following verb starts with a vowel?
Looks like it's both "nu au" or n-au" - here we read the former, and the answer given to the English has the latter? Hoping a Romanian native speaker will tell us!
Both are correct. 'N-au' tends to be found more in informal speech.
You should only use this contraction for verbs that starts with 'a-'.