"Non, tu bois l'eau."
That means "you don't drink the water." That means something entirely different than saying "no, you drink the water."
Sorry, I really should've put this in reply to Mariooooooo rather than just mentioning their name at the end of the message. They asked "How would you say, 'you don't drink the water?'" Sorry about the confusion. :)
Another correct answer: "No, you are eating the water." No, I don't think so duolingo...no one ever eats water.
Does this also mean you don't drink the water? How would you say, 'you don't drink the water?'
No, this just means "No, you are drinking the water". To say "You don't drink the water" you would say "Tu ne bois pas d'eau" (After a negative (ne.....pas) you must use 'de' not 'le/la/les')
Here it's "Non, tu bois l'eau" so the negative form would be "Non, tu ne bois pas l'eau". There isn't always "de" after a negative form! "Tu bois l'eau" probably refers to a specific glass of water here. Saying "tu ne bois pas d'eau" would mean the person shouldn't drink water at all, whether it in the glass or not.