I dont get it!!!! (a question about walmart and food)

Question

I've been trying to use my Spanish where ever I can, and that includes grocery shopping mommy So when ever she tells me "I need a watermelon," or "I need a pineapple'" I say to her "necesitas una sandía," or "Necesitas una piña?" She then starts yelling at me because for some odd reason she does not like me speaking spanish...EVER! But thats not, the problem is i was in walmart yesterday and i was reading nestle's water packaging and It says (in english) "Drink 3 bottles a day!" in Spanish it says "Bebe 3 botellas al día!" I am confused about 2 things. Shoudn't bebe be bebes because its telling YOU to drink 3 times a day. And why is it AL DíA" instead of UNA DíA. Someone please help me

THANKS IN ADVANCE!!!!

Answer 1

Bebe is the imperative form for tú.

Al día means per day, un día means one day (día is masculine.)