I learned this the hard way last year. If you're hunting in an area with lots of bear activity, it's a great idea to stash your food and water up in a tree. I like to wrap everything in a tarp and tie it between two trees. Don't just tie it up in one tree but tie it in between two trees at least 15 feet in the air. I thought I had my backpacking camp's food supply stashed pretty well last year. I returned to camp during the first weekend of archery to find all my food destroyed. Make sure you get it far enough out that a bear can't reach it because if you don't you'll end up like me last season.
I didn't tie the bag full of food far enough between the two trees and a bear was able to climb up and eat everything including my water bottles.