you can’t take a bottle with you inside…that is after checking in. however, you can take the water bottle that they give you in planes out of the planes, and that’s usually as big as a cup. and that’s not always enough when you’re coming out thirsty on a 7-8 hour flight. but. not all of the airports have water fountains. i found out this the hard way. and not all the water fountains have exactly the purest of the drinkable water.