They are great, but what if you already have a reusable plastic bottle? Do you have to toss it? We've got some good news! You don't have to throw it away or relegate it to sitting at the back of the cabinet, you just have to be smart about when and how you use it. Don't let water sit in it for weeks and don't let it bake in the sun. For more tips on safely using your beloved plastic water bottle, check out our full list of tips.