Replying to Is this illegal?

I brought a gallon of water into a movie theatre and one of the workers told me to throw it away, or he’d confiscate it. Under what authority are they allowed to do this. I would of happily said okay if I could have had water from the movie theater but you have to pay a ridiculous amount for it.

I find it very concerning that companies force you to buy their water, and will even get the police involved if you bring water that isn’t theirs. Seems kind of draconian to me.