You can eat popcorn and drink water.
I always eat popcorn and drink water when I do eat popcorn as it helps aid in digestion and also help with the saltiness that can lead to dry mouth when eating salty popcorn.
Popcorn also has high fiber content, which can lead to constipation or bloating if you don't drink water with the popcorn, so it's recommended to drink water when eating popcorn.
Although it's also always best to drink water throughout the time you're eating the popcorn, instead of just drinking the water after eating the popcorn.
Drinking water helps the fiber in the popcorn move through your digestive tract and promotes regular bowel movements.
And without enough water, the high fiber in the popcorn can lead to constipation and discomfort.
Sip some water gradually as you eat the popcorn which can help with digestion and prevent drying of the mouth from the saltiness and also helps to move the popcorn down your throat and into your stomach.